--- a/libcxx/include/wchar.h	Wed Jul 21 10:27:27 2021 +0900
+++ b/libcxx/include/wchar.h	Wed Nov 09 17:45:10 2022 +0900
@@ -1,5 +1,5 @@
 // -*- C++ -*-
-//===--------------------------- wchar.h ----------------------------------===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -10,7 +10,7 @@
 #if defined(__need_wint_t) || defined(__need_mbstate_t)
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#pragma GCC system_header
+#  pragma GCC system_header
 #endif
 
 #include_next <wchar.h>
@@ -108,8 +108,12 @@
 #include <__config>
 #include <stddef.h>
 
+#if defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS)
+#   error "The <wchar.h> header is not supported since libc++ has been configured with LIBCXX_ENABLE_WIDE_CHARACTERS disabled"
+#endif
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#pragma GCC system_header
+#  pragma GCC system_header
 #endif
 
 #ifdef __cplusplus
@@ -170,13 +174,13 @@
 }
 #endif
 
-#if defined(__cplusplus) && defined(_LIBCPP_MSVCRT_LIKE)
+#if defined(__cplusplus) && (defined(_LIBCPP_MSVCRT_LIKE) || defined(__MVS__))
 extern "C" {
-size_t mbsnrtowcs(wchar_t *__restrict dst, const char **__restrict src,
-                  size_t nmc, size_t len, mbstate_t *__restrict ps);
-size_t wcsnrtombs(char *__restrict dst, const wchar_t **__restrict src,
-                  size_t nwc, size_t len, mbstate_t *__restrict ps);
-}  // extern "C++"
-#endif // __cplusplus && _LIBCPP_MSVCRT
+size_t mbsnrtowcs(wchar_t *__restrict __dst, const char **__restrict __src,
+                  size_t __nmc, size_t __len, mbstate_t *__restrict __ps);
+size_t wcsnrtombs(char *__restrict __dst, const wchar_t **__restrict __src,
+                  size_t __nwc, size_t __len, mbstate_t *__restrict __ps);
+}  // extern "C"
+#endif  // __cplusplus && (_LIBCPP_MSVCRT || __MVS__)
 
 #endif // _LIBCPP_WCHAR_H