Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__mbstate_t.h

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+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MBSTATE_T_H
+#define _LIBCPP___MBSTATE_T_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+// The goal of this header is to provide mbstate_t without requiring all of
+// <uchar.h> or <wchar.h>. It's also used by the libc++ versions of <uchar.h>
+// and <wchar.h> to get mbstate_t when the C library doesn't provide <uchar.h>
+// or <wchar.h>, hence the #include_next of those headers instead of #include.
+// (e.g. if <wchar.h> isn't present in the C library, the libc++ <wchar.h>
+// will include this header. This header needs to not turn around and cyclically
+// include <wchar.h>, but fall through to <uchar.h>.)
+//
+// This does not define std::mbstate_t -- this only brings in the declaration
+// in the global namespace.
+
+// We define this here to support older versions of glibc <wchar.h> that do
+// not define this for clang. This is also set in libc++'s <wchar.h> header,
+// and we need to do so here too to avoid a different function signature given
+// a different include order.
+#ifdef __cplusplus
+#  define __CORRECT_ISO_CPP_WCHAR_H_PROTO
+#endif
+
+#if defined(_LIBCPP_HAS_MUSL_LIBC)
+#   define __NEED_mbstate_t
+#   include <bits/alltypes.h>
+#   undef __NEED_mbstate_t
+#elif __has_include(<bits/types/mbstate_t.h>)
+#   include <bits/types/mbstate_t.h> // works on most Unixes
+#elif __has_include(<sys/_types/_mbstate_t.h>)
+#   include <sys/_types/_mbstate_t.h> // works on Darwin
+#elif !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS) && __has_include_next(<wchar.h>)
+#   include_next <wchar.h> // fall back to the C standard provider of mbstate_t
+#elif __has_include_next(<uchar.h>)
+#   include_next <uchar.h> // <uchar.h> is also required to make mbstate_t visible
+#else
+#   error "We don't know how to get the definition of mbstate_t without <wchar.h> on your platform."
+#endif
+
+#endif // _LIBCPP___MBSTATE_T_H