--- a/libcxx/include/cstddef	Wed Jul 21 10:27:27 2021 +0900
+++ b/libcxx/include/cstddef	Wed Nov 09 17:45:10 2022 +0900
@@ -1,5 +1,5 @@
 // -*- C++ -*-
-//===--------------------------- cstddef ----------------------------------===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -33,19 +33,30 @@
 
 */
 
+#include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/is_integral.h>
 #include <version>
 
+#include <stddef.h>
+
+#ifndef _LIBCPP_STDDEF_H
+#   error <cstddef> tried including <stddef.h> but didn't find libc++'s <stddef.h> header. \
+          This usually means that your header search paths are not configured properly. \
+          The header search paths should contain the C++ Standard Library headers before \
+          any C Standard Library, and you are probably using compiler flags that make that \
+          not be the case.
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#pragma GCC system_header
+#  pragma GCC system_header
 #endif
 
-// Don't include our own <stddef.h>; we don't want to declare ::nullptr_t.
-#include_next <stddef.h>
-#include <__nullptr>
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+using ::nullptr_t;
 using ::ptrdiff_t _LIBCPP_USING_IF_EXISTS;
 using ::size_t _LIBCPP_USING_IF_EXISTS;
 
@@ -53,32 +64,6 @@
 using ::max_align_t _LIBCPP_USING_IF_EXISTS;
 #endif
 
-template <class _Tp> struct __libcpp_is_integral                     { enum { value = 0 }; };
-template <>          struct __libcpp_is_integral<bool>               { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<char>               { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<signed char>        { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<unsigned char>      { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<wchar_t>            { enum { value = 1 }; };
-#ifndef _LIBCPP_HAS_NO_CHAR8_T
-template <>          struct __libcpp_is_integral<char8_t>            { enum { value = 1 }; };
-#endif
-#ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
-template <>          struct __libcpp_is_integral<char16_t>           { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<char32_t>           { enum { value = 1 }; };
-#endif // _LIBCPP_HAS_NO_UNICODE_CHARS
-template <>          struct __libcpp_is_integral<short>              { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<unsigned short>     { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<int>                { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<unsigned int>       { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<long>               { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<unsigned long>      { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<long long>          { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<unsigned long long> { enum { value = 1 }; };
-#ifndef _LIBCPP_HAS_NO_INT128
-template <>          struct __libcpp_is_integral<__int128_t>         { enum { value = 1 }; };
-template <>          struct __libcpp_is_integral<__uint128_t>        { enum { value = 1 }; };
-#endif
-
 _LIBCPP_END_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 14
@@ -86,12 +71,7 @@
 {
 enum class byte : unsigned char {};
 
-
-template <bool> struct __enable_if_integral_imp {};
-template <> struct __enable_if_integral_imp<true> { using type = byte; };
-template <class _Tp> using _EnableByteOverload = typename __enable_if_integral_imp<__libcpp_is_integral<_Tp>::value>::type;
-
-constexpr byte  operator| (byte  __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte  operator| (byte  __lhs, byte __rhs) noexcept
 {
     return static_cast<byte>(
       static_cast<unsigned char>(
@@ -99,10 +79,10 @@
     ));
 }
 
-constexpr byte& operator|=(byte& __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte& operator|=(byte& __lhs, byte __rhs) noexcept
 { return __lhs = __lhs | __rhs; }
 
-constexpr byte  operator& (byte  __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte  operator& (byte  __lhs, byte __rhs) noexcept
 {
     return static_cast<byte>(
       static_cast<unsigned char>(
@@ -110,10 +90,10 @@
     ));
 }
 
-constexpr byte& operator&=(byte& __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte& operator&=(byte& __lhs, byte __rhs) noexcept
 { return __lhs = __lhs & __rhs; }
 
-constexpr byte  operator^ (byte  __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte  operator^ (byte  __lhs, byte __rhs) noexcept
 {
     return static_cast<byte>(
       static_cast<unsigned char>(
@@ -121,40 +101,45 @@
     ));
 }
 
-constexpr byte& operator^=(byte& __lhs, byte __rhs) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte& operator^=(byte& __lhs, byte __rhs) noexcept
 { return __lhs = __lhs ^ __rhs; }
 
-constexpr byte  operator~ (byte __b) noexcept
+_LIBCPP_HIDE_FROM_ABI constexpr byte  operator~ (byte __b) noexcept
 {
     return static_cast<byte>(
       static_cast<unsigned char>(
         ~static_cast<unsigned int>(__b)
     ));
 }
+
+template <class _Tp>
+using _EnableByteOverload = __enable_if_t<is_integral<_Tp>::value, byte>;
+
 template <class _Integer>
-  constexpr _EnableByteOverload<_Integer> &
+_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer> &
   operator<<=(byte& __lhs, _Integer __shift) noexcept
   { return __lhs = __lhs << __shift; }
 
 template <class _Integer>
-  constexpr _EnableByteOverload<_Integer>
+_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer>
   operator<< (byte  __lhs, _Integer __shift) noexcept
   { return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) << __shift)); }
 
 template <class _Integer>
-  constexpr _EnableByteOverload<_Integer> &
+_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer> &
   operator>>=(byte& __lhs, _Integer __shift) noexcept
   { return __lhs = __lhs >> __shift; }
 
 template <class _Integer>
-  constexpr _EnableByteOverload<_Integer>
+_LIBCPP_HIDE_FROM_ABI constexpr _EnableByteOverload<_Integer>
   operator>> (byte  __lhs, _Integer __shift) noexcept
   { return static_cast<byte>(static_cast<unsigned char>(static_cast<unsigned int>(__lhs) >> __shift)); }
 
 template <class _Integer, class = _EnableByteOverload<_Integer> >
-  _LIBCPP_NODISCARD_EXT constexpr _Integer
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Integer
   to_integer(byte __b) noexcept { return static_cast<_Integer>(__b); }
-}
+
+} // namespace std
 
 #endif