--- a/libcxx/CMakeLists.txt	Wed Nov 09 17:47:54 2022 +0900
+++ b/libcxx/CMakeLists.txt	Fri Aug 18 09:04:13 2023 +0900
@@ -4,7 +4,7 @@
 #===============================================================================
 # Setup Project
 #===============================================================================
-cmake_minimum_required(VERSION 3.13.4)
+cmake_minimum_required(VERSION 3.20.0)
 
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
@@ -12,6 +12,7 @@
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"
+  "${CMAKE_CURRENT_SOURCE_DIR}/../runtimes/cmake/Modules"
   "${LLVM_COMMON_CMAKE_UTILS}"
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
@@ -23,6 +24,7 @@
 set(LIBCXX_BINARY_INCLUDE_DIR "${LIBCXX_BINARY_DIR}/include/c++build")
 
 include(GNUInstallDirs)
+include(WarningFlags)
 
 # Require out of source build.
 include(MacroEnsureOutOfSourceBuild)
@@ -36,10 +38,7 @@
 endif()
 
 if (MSVC)
-  set(LIBCXX_TARGETING_MSVC ON)
   message(STATUS "Configuring for MSVC")
-else()
-  set(LIBCXX_TARGETING_MSVC OFF)
 endif()
 
 #===============================================================================
@@ -49,29 +48,23 @@
 include(HandleCompilerRT)
 
 # Basic options ---------------------------------------------------------------
-option(LIBCXX_ENABLE_ASSERTIONS
-  "Enable assertions inside the compiled library, and at the same time make it the
-   default when compiling user code. Note that assertions can be enabled or disabled
-   by users in their own code regardless of this option." OFF)
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
 option(LIBCXX_ENABLE_STATIC "Build libc++ as a static library." ON)
-set(ENABLE_FILESYSTEM_DEFAULT ON)
-if (WIN32 AND NOT MINGW)
-  # Filesystem is buildable for windows, but it requires __int128 helper
-  # functions, that currently are provided by libgcc or compiler_rt builtins.
-  # These are available in MinGW environments, but not currently in MSVC
-  # environments.
-  set(ENABLE_FILESYSTEM_DEFAULT OFF)
+option(LIBCXX_ENABLE_FILESYSTEM
+  "Whether to include support for parts of the library that rely on a filesystem being
+   available on the platform. This includes things like most parts of <filesystem> and
+   others like <fstream>" ON)
+option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
+set(LIBCXX_SUPPORTED_HARDENING_MODES unchecked hardened debug)
+set(LIBCXX_HARDENING_MODE "unchecked" CACHE STRING
+  "Specify the default hardening mode to use. This mode will be used inside the
+   compiled library and will be the default when compiling user code. Note that
+   users can override this setting in their own code. This does not affect the
+   ABI. Supported values are ${LIBCXX_SUPPORTED_HARDENING_MODES}.")
+if (NOT "${LIBCXX_HARDENING_MODE}" IN_LIST LIBCXX_SUPPORTED_HARDENING_MODES)
+  message(FATAL_ERROR
+    "Unsupported hardening mode: '${LIBCXX_HARDENING_MODE}'. Supported values are ${LIBCXX_SUPPORTED_HARDENING_MODES}.")
 endif()
-option(LIBCXX_ENABLE_FILESYSTEM "Build filesystem as part of the main libc++ library"
-    ${ENABLE_FILESYSTEM_DEFAULT})
-option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
-option(LIBCXX_ENABLE_PARALLEL_ALGORITHMS "Enable the parallel algorithms library. This requires the PSTL to be available." OFF)
-option(LIBCXX_ENABLE_DEBUG_MODE
-  "Whether to build libc++ with the debug mode enabled.
-   By default, this is turned off. Turning it on results in a different ABI (additional
-   symbols but also potentially different layouts of types), and one should not mix code
-   built against a dylib that has debug mode and code built against a regular dylib." OFF)
 option(LIBCXX_ENABLE_RANDOM_DEVICE
   "Whether to include support for std::random_device in the library. Disabling
    this can be useful when building the library for platforms that don't have
@@ -101,6 +94,13 @@
    to provide compile-time errors when using features unavailable on some version of
    the shared library they shipped should turn this on and see `include/__availability`
    for more details." OFF)
+option(LIBCXX_ENABLE_CLANG_TIDY "Whether to compile and run clang-tidy checks" OFF)
+# TODO MODULES Remove this option and test for the requirements (CMake/Clang) instead.
+option(LIBCXX_ENABLE_STD_MODULES
+   "Whether to enable the building the C++23 `std` module. This feature is
+    experimental and has additional dependencies. Only enable this when
+    interested in testing or developing this module. See
+    https://libcxx.llvm.org/Modules.html for more information." OFF)
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   set(LIBCXX_DEFAULT_TEST_CONFIG "llvm-libc++-shared-gcc.cfg.in")
@@ -200,15 +200,8 @@
 option(LIBCXX_EXTRA_SITE_DEFINES "Extra defines to add into __config_site")
 option(LIBCXX_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 
-option(LIBCXX_ENABLE_BACKWARDS_COMPATIBILITY_DEBUG_MODE_SYMBOLS
-  "Whether to include the old Debug mode symbols in the compiled library. This
-   is provided for backwards compatibility since the compiled library used to
-   always contain those symbols, regardless of whether the library was built
-   with the debug mode enabled. This is OFF by default, please contact the libc++
-   developers if you need to turn this on, as this will be removed in LLVM 16." OFF)
-
 # ABI Library options ---------------------------------------------------------
-if (LIBCXX_TARGETING_MSVC)
+if (MSVC)
   set(LIBCXX_DEFAULT_ABI_LIBRARY "vcruntime")
 elseif (${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
   set(LIBCXX_DEFAULT_ABI_LIBRARY "libcxxrt")
@@ -266,11 +259,6 @@
   message(FATAL_ERROR "LIBCXX_BUILD_32_BITS is not supported anymore when building the runtimes, please specify a full triple instead.")
 endif()
 
-# TODO: Remove this after branching for LLVM 15
-if(LIBCXX_SYSROOT OR LIBCXX_TARGET_TRIPLE OR LIBCXX_GCC_TOOLCHAIN)
-  message(WARNING "LIBCXX_SYSROOT, LIBCXX_TARGET_TRIPLE and LIBCXX_GCC_TOOLCHAIN are not supported anymore, please use the native CMake equivalents instead")
-endif()
-
 # Feature options -------------------------------------------------------------
 option(LIBCXX_ENABLE_EXCEPTIONS "Use exceptions." ON)
 option(LIBCXX_ENABLE_RTTI "Use run time type information." ON)
@@ -284,9 +272,12 @@
 option(LIBCXX_HAS_EXTERNAL_THREAD_API
   "Build libc++ with an externalized threading API.
    This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON." OFF)
-option(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY
-    "Build libc++ with an externalized threading library.
-     This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON" OFF)
+
+if (LIBCXX_ENABLE_THREADS)
+  set(LIBCXX_PSTL_CPU_BACKEND "std_thread" CACHE STRING "Which PSTL CPU backend to use")
+else()
+  set(LIBCXX_PSTL_CPU_BACKEND "serial" CACHE STRING "Which PSTL CPU backend to use")
+endif()
 
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
@@ -333,10 +324,6 @@
     message(FATAL_ERROR "LIBCXX_HAS_EXTERNAL_THREAD_API can only be set to ON"
                         " when LIBCXX_ENABLE_THREADS is also set to ON.")
   endif()
-  if (LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
-    message(FATAL_ERROR "LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY can only be set "
-                        "to ON when LIBCXX_ENABLE_THREADS is also set to ON.")
-  endif()
   if (LIBCXX_HAS_WIN32_THREAD_API)
     message(FATAL_ERROR "LIBCXX_HAS_WIN32_THREAD_API can only be set to ON"
                         " when LIBCXX_ENABLE_THREADS is also set to ON.")
@@ -345,11 +332,6 @@
 endif()
 
 if (LIBCXX_HAS_EXTERNAL_THREAD_API)
-  if (LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
-    message(FATAL_ERROR "The options LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY and "
-                        "LIBCXX_HAS_EXTERNAL_THREAD_API cannot both be ON at "
-                        "the same time")
-  endif()
   if (LIBCXX_HAS_PTHREAD_API)
     message(FATAL_ERROR "The options LIBCXX_HAS_EXTERNAL_THREAD_API"
                         "and LIBCXX_HAS_PTHREAD_API cannot be both"
@@ -395,6 +377,11 @@
   message(FATAL_ERROR "Only one of LIBCXX_ABI_FORCE_ITANIUM and LIBCXX_ABI_FORCE_MICROSOFT can be specified.")
 endif ()
 
+if (LIBCXX_ENABLE_SHARED AND CMAKE_MSVC_RUNTIME_LIBRARY AND
+    (NOT CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$"))
+  message(WARNING "A static CRT linked into a shared libc++ doesn't work correctly.")
+endif()
+
 #===============================================================================
 # Configure System
 #===============================================================================
@@ -413,6 +400,7 @@
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE})
   set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
+  set(LIBCXX_GENERATED_MODULE_DIR "${LLVM_BINARY_DIR}/modules/c++/v1")
   set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LLVM_BINARY_DIR}/include/${LLVM_DEFAULT_TARGET_TRIPLE}/c++/v1")
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE} CACHE PATH
       "Path where built libc++ libraries should be installed.")
@@ -426,9 +414,11 @@
   if(LLVM_LIBRARY_OUTPUT_INTDIR)
     set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
     set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
+    set(LIBCXX_GENERATED_MODULE_DIR "${LLVM_BINARY_DIR}/modules/c++/v1")
   else()
     set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})
     set(LIBCXX_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
+    set(LIBCXX_GENERATED_MODULE_DIR "${CMAKE_BINARY_DIR}/modules/c++/v1")
   endif()
   set(LIBCXX_GENERATED_INCLUDE_TARGET_DIR "${LIBCXX_GENERATED_INCLUDE_DIR}")
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX} CACHE PATH
@@ -466,7 +456,7 @@
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
 
 if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
-  add_target_flags_if_supported("-mdefault-visibility-export-mapping=explicit")
+  add_flags_if_supported("-mdefault-visibility-export-mapping=explicit")
   set(CMAKE_AIX_EXPORT_ALL_SYMBOLS OFF)
 endif()
 
@@ -479,30 +469,12 @@
   set(CMAKE_BUILD_TYPE "COVERAGE" CACHE STRING "" FORCE)
 endif()
 
-string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
-if (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
-  set(LIBCXX_DEBUG_BUILD ON)
-else()
-  set(LIBCXX_DEBUG_BUILD OFF)
-endif()
-
 #===============================================================================
 # Setup Compiler Flags
 #===============================================================================
 
 include(HandleLibCXXABI) # Setup the ABI library flags
 
-# Remove flags that may have snuck in.
-# TODO: This shouldn't be necessary anymore since we don't support the Project
-#       build anymore, so the rest of LLVM can't pollute our flags.
-remove_flags(-DNDEBUG -UNDEBUG -D_DEBUG -lc++abi)
-remove_flags(--stdlib=libc++ -stdlib=libc++ --stdlib=libstdc++ -stdlib=libstdc++)
-
-# FIXME: Remove all debug flags and flags that change which Windows
-# default libraries are linked. Currently we only support linking the
-# non-debug DLLs
-remove_flags("/D_DEBUG" "/MTd" "/MDd" "/MT" "/Md")
-
 # FIXME(EricWF): See the FIXME on LIBCXX_ENABLE_PEDANTIC.
 # Remove the -pedantic flag and -Wno-pedantic and -pedantic-errors
 # so they don't get transformed into -Wno and -errors respectively.
@@ -546,18 +518,14 @@
     target_add_compile_flags_if_supported(${target} PRIVATE -fvisibility=hidden)
   endif()
 
-  if (LIBCXX_CONFIGURE_IDE)
-    # This simply allows IDE to process <experimental/coroutine>
-    target_add_compile_flags_if_supported(${target} PRIVATE -fcoroutines-ts)
-  endif()
-
   # Let the library headers know they are currently being used to build the
   # library.
   target_compile_definitions(${target} PRIVATE -D_LIBCPP_BUILDING_LIBRARY)
 
-  if (NOT LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS)
-    target_compile_definitions(${target} PRIVATE -D_LIBCPP_DISABLE_NEW_DELETE_DEFINITIONS)
-  endif()
+  # Make sure the library can be build without transitive includes. This makes
+  # it easier to upgrade the library to a newer language standard without build
+  # errors.
+  target_compile_definitions(${target} PRIVATE -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES)
 
   if (C_SUPPORTS_COMMENT_LIB_PRAGMA)
     if (LIBCXX_HAS_PTHREAD_LIB)
@@ -570,65 +538,6 @@
   target_compile_options(${target} PUBLIC "${LIBCXX_ADDITIONAL_COMPILE_FLAGS}")
 endfunction()
 
-# Warning flags ===============================================================
-function(cxx_add_warning_flags target)
-  target_compile_definitions(${target} PUBLIC -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-  if (MSVC)
-    # -W4 is the cl.exe/clang-cl equivalent of -Wall. (In cl.exe and clang-cl,
-    # -Wall is equivalent to -Weverything in GCC style compiler drivers.)
-    target_add_compile_flags_if_supported(${target} PRIVATE -W4)
-  else()
-    target_add_compile_flags_if_supported(${target} PRIVATE -Wall)
-  endif()
-  target_add_compile_flags_if_supported(${target} PRIVATE -Wextra -W -Wwrite-strings
-                                                          -Wno-unused-parameter -Wno-long-long
-                                                          -Werror=return-type -Wextra-semi -Wundef
-                                                          -Wformat-nonliteral)
-  if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
-    target_add_compile_flags_if_supported(${target} PRIVATE
-      -Wno-user-defined-literals
-      -Wno-covered-switch-default
-      -Wno-suggest-override
-    )
-    if (LIBCXX_TARGETING_CLANG_CL)
-      target_add_compile_flags_if_supported(${target} PRIVATE
-        -Wno-c++98-compat
-        -Wno-c++98-compat-pedantic
-        -Wno-c++11-compat
-        -Wno-undef
-        -Wno-reserved-id-macro
-        -Wno-gnu-include-next
-        -Wno-gcc-compat # For ignoring "'diagnose_if' is a clang extension" warnings
-        -Wno-zero-as-null-pointer-constant # FIXME: Remove this and fix all occurrences.
-        -Wno-deprecated-dynamic-exception-spec # For auto_ptr
-        -Wno-sign-conversion
-        -Wno-old-style-cast
-        -Wno-deprecated # FIXME: Remove this and fix all occurrences.
-        -Wno-shift-sign-overflow # FIXME: Why do we need this with clang-cl but not clang?
-        -Wno-double-promotion # FIXME: remove me
-      )
-    endif()
-  elseif("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
-    target_add_compile_flags_if_supported(${target} PRIVATE
-      -Wno-attributes
-      -Wno-literal-suffix
-      -Wno-c++14-compat
-      -Wno-noexcept-type
-      -Wno-suggest-override)
-  endif()
-  if (LIBCXX_ENABLE_WERROR)
-    target_add_compile_flags_if_supported(${target} PRIVATE -Werror)
-    target_add_compile_flags_if_supported(${target} PRIVATE -WX)
-  else()
-    # TODO(EricWF) Remove this. We shouldn't be suppressing errors when -Werror is
-    # added elsewhere.
-    target_add_compile_flags_if_supported(${target} PRIVATE -Wno-error)
-  endif()
-  if (LIBCXX_ENABLE_PEDANTIC)
-    target_add_compile_flags_if_supported(${target} PRIVATE -pedantic)
-  endif()
-endfunction()
-
 # Exception flags =============================================================
 function(cxx_add_exception_flags target)
   if (LIBCXX_ENABLE_EXCEPTIONS)
@@ -644,29 +553,14 @@
 # RTTI flags ==================================================================
 function(cxx_add_rtti_flags target)
   if (NOT LIBCXX_ENABLE_RTTI)
-    target_add_compile_flags_if_supported(${target} PUBLIC -GR-)
-    target_add_compile_flags_if_supported(${target} PUBLIC -fno-rtti)
+    if (MSVC)
+      target_add_compile_flags_if_supported(${target} PUBLIC -GR-)
+    else()
+      target_add_compile_flags_if_supported(${target} PUBLIC -fno-rtti)
+    endif()
   endif()
 endfunction()
 
-# Threading flags =============================================================
-if (LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY AND LIBCXX_ENABLE_SHARED)
-  # Need to allow unresolved symbols if this is to work with shared library builds
-  if (APPLE)
-    add_link_flags("-undefined dynamic_lookup")
-  else()
-    # Relax this restriction from HandleLLVMOptions
-    string(REPLACE "-Wl,-z,defs" "" CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}")
-  endif()
-endif()
-
-# Assertion flags =============================================================
-define_if(LIBCXX_DEBUG_BUILD -D_DEBUG)
-if (LIBCXX_ENABLE_ASSERTIONS AND NOT LIBCXX_DEBUG_BUILD)
-  # MSVC doesn't like _DEBUG on release builds. See PR 4379.
-  define_if_not(LIBCXX_TARGETING_MSVC -D_DEBUG)
-endif()
-
 # Modules flags ===============================================================
 # FIXME The libc++ sources are fundamentally non-modular. They need special
 # versions of the headers in order to provide C++03 and legacy ABI definitions.
@@ -679,6 +573,8 @@
   endif()
 endfunction()
 
+string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+
 # Sanitizer flags =============================================================
 
 function(get_sanitizer_flags OUT_VAR  USE_SANITIZER)
@@ -785,17 +681,24 @@
     target_link_libraries(${target} PRIVATE "${MINGW_LIBRARIES}")
   endif()
 
-  if (LIBCXX_TARGETING_MSVC)
-    if (LIBCXX_DEBUG_BUILD)
+  if (MSVC)
+    if ((NOT CMAKE_MSVC_RUNTIME_LIBRARY AND uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+        OR (CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "Debug"))
       set(LIB_SUFFIX "d")
     else()
       set(LIB_SUFFIX "")
     endif()
 
-    target_link_libraries(${target} PRIVATE ucrt${LIB_SUFFIX}) # Universal C runtime
-    target_link_libraries(${target} PRIVATE vcruntime${LIB_SUFFIX}) # C++ runtime
-    target_link_libraries(${target} PRIVATE msvcrt${LIB_SUFFIX}) # C runtime startup files
-    target_link_libraries(${target} PRIVATE msvcprt${LIB_SUFFIX}) # C++ standard library. Required for exception_ptr internals.
+    if (NOT CMAKE_MSVC_RUNTIME_LIBRARY OR CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$")
+      set(CRT_LIB "msvcrt")
+      set(CXX_LIB "msvcprt")
+    else()
+      set(CRT_LIB "libcmt")
+      set(CXX_LIB "libcpmt")
+    endif()
+
+    target_link_libraries(${target} PRIVATE ${CRT_LIB}${LIB_SUFFIX}) # C runtime startup files
+    target_link_libraries(${target} PRIVATE ${CXX_LIB}${LIB_SUFFIX}) # C++ standard library. Required for exception_ptr internals.
     # Required for standards-complaint wide character formatting functions
     # (e.g. `printfw`/`scanfw`)
     target_link_libraries(${target} PRIVATE iso_stdio_wide_specifiers)
@@ -829,14 +732,6 @@
                                  # Use the ISO conforming behaviour for conversion
                                  # in printf, scanf.
                                  _CRT_STDIO_ISO_WIDE_SPECIFIERS)
-    # Clang-cl shared builds don't support the experimental library.
-    # To avoid linker errors the format_error destructor is inlined for the
-    # dylib. Users can never use format in this mode.
-    # TODO FMT Remove when format becomes mainline.
-    if (LIBCXX_ENABLE_SHARED)
-      target_compile_definitions(${target} PRIVATE
-                                 _LIBCPP_INLINE_FORMAT_ERROR_DTOR)
-    endif()
   endif()
 endfunction()
 
@@ -853,21 +748,39 @@
 config_define_if(LIBCXX_HAS_PTHREAD_API _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define_if(LIBCXX_HAS_EXTERNAL_THREAD_API _LIBCPP_HAS_THREAD_API_EXTERNAL)
 config_define_if(LIBCXX_HAS_WIN32_THREAD_API _LIBCPP_HAS_THREAD_API_WIN32)
-config_define_if(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
 config_define_if(LIBCXX_HAS_MUSL_LIBC _LIBCPP_HAS_MUSL_LIBC)
 config_define_if(LIBCXX_NO_VCRUNTIME _LIBCPP_NO_VCRUNTIME)
-config_define_if(LIBCXX_ENABLE_PARALLEL_ALGORITHMS _LIBCPP_HAS_PARALLEL_ALGORITHMS)
-config_define_if_not(LIBCXX_ENABLE_FILESYSTEM _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY)
+config_define_if_not(LIBCXX_ENABLE_FILESYSTEM _LIBCPP_HAS_NO_FILESYSTEM)
 config_define_if_not(LIBCXX_ENABLE_RANDOM_DEVICE _LIBCPP_HAS_NO_RANDOM_DEVICE)
 config_define_if_not(LIBCXX_ENABLE_LOCALIZATION _LIBCPP_HAS_NO_LOCALIZATION)
 config_define_if_not(LIBCXX_ENABLE_UNICODE _LIBCPP_HAS_NO_UNICODE)
 config_define_if_not(LIBCXX_ENABLE_WIDE_CHARACTERS _LIBCPP_HAS_NO_WIDE_CHARACTERS)
 config_define_if_not(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
-config_define_if(LIBCXX_ENABLE_DEBUG_MODE _LIBCPP_ENABLE_DEBUG_MODE)
+if (LIBCXX_HARDENING_MODE STREQUAL "hardened")
+  config_define(1 _LIBCPP_ENABLE_HARDENED_MODE_DEFAULT)
+  config_define(0 _LIBCPP_ENABLE_DEBUG_MODE_DEFAULT)
+elseif (LIBCXX_HARDENING_MODE STREQUAL "debug")
+  config_define(0 _LIBCPP_ENABLE_HARDENED_MODE_DEFAULT)
+  config_define(1 _LIBCPP_ENABLE_DEBUG_MODE_DEFAULT)
+elseif (LIBCXX_HARDENING_MODE STREQUAL "unchecked")
+  config_define(0 _LIBCPP_ENABLE_HARDENED_MODE_DEFAULT)
+  config_define(0 _LIBCPP_ENABLE_DEBUG_MODE_DEFAULT)
+endif()
+# TODO(LLVM 18): Remove this after branching for LLVM 17, this is a simple
+# courtesy for vendors to be notified about this change.
 if (LIBCXX_ENABLE_ASSERTIONS)
-  config_define(1 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT)
+  message(FATAL_ERROR "LIBCXX_ENABLE_ASSERTIONS has been replaced by LIBCXX_HARDENING_MODE=hardened")
+endif()
+
+if (LIBCXX_PSTL_CPU_BACKEND STREQUAL "serial")
+  config_define(1 _LIBCPP_PSTL_CPU_BACKEND_SERIAL)
+elseif(LIBCXX_PSTL_CPU_BACKEND STREQUAL "std_thread")
+  config_define(1 _LIBCPP_PSTL_CPU_BACKEND_THREAD)
+elseif(LIBCXX_PSTL_CPU_BACKEND STREQUAL "libdispatch")
+  config_define(1 _LIBCPP_PSTL_CPU_BACKEND_LIBDISPATCH)
 else()
-  config_define(0 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT)
+  message(FATAL_ERROR "LIBCXX_PSTL_CPU_BACKEND is set to ${LIBCXX_PSTL_CPU_BACKEND}, which is not a valid backend.
+                       Valid backends are: serial, std_thread and libdispatch")
 endif()
 
 if (LIBCXX_ABI_DEFINES)
@@ -910,7 +823,7 @@
 # Setup all common build flags =================================================
 function(cxx_add_common_build_flags target)
   cxx_add_basic_build_flags(${target})
-  cxx_add_warning_flags(${target})
+  cxx_add_warning_flags(${target} ${LIBCXX_ENABLE_WERROR} ${LIBCXX_ENABLE_PEDANTIC})
   cxx_add_windows_flags(${target})
   cxx_add_exception_flags(${target})
   cxx_add_rtti_flags(${target})
@@ -924,11 +837,18 @@
 add_subdirectory(include)
 add_subdirectory(src)
 add_subdirectory(utils)
+if (LIBCXX_ENABLE_STD_MODULES)
+  add_subdirectory(modules)
+endif()
 
 set(LIBCXX_TEST_DEPS "cxx_experimental")
 
-if (LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
-  list(APPEND LIBCXX_TEST_DEPS cxx_external_threads)
+if (LIBCXX_ENABLE_CLANG_TIDY)
+  list(APPEND LIBCXX_TEST_DEPS cxx-tidy)
+endif()
+
+if (LIBCXX_ENABLE_STD_MODULES)
+  list(APPEND LIBCXX_TEST_DEPS generate-cxx-modules generate-test-module-std)
 endif()
 
 if (LIBCXX_INCLUDE_BENCHMARKS)