[libc++][C++03] Use __cxx03/ headers in C++03 mode

Author: philnik777

.github/workflows/libcxx-build-and-test.yaml

@@ -55,6 +55,7 @@ jobs:
       fail-fast: false
       matrix:
         config: [
+          'cxx03-main-headers',
           'generic-cxx03',
           'generic-cxx26',
           'generic-modules'

libcxx/cmake/caches/cxx03-headers.cmake

@@ -0,0 +1,2 @@
+set(LIBCXX_TEST_PARAMS "std=c++03;test-cxx03-headers=True" CACHE STRING "")
+set(LIBCXXABI_TEST_PARAMS "${LIBCXX_TEST_PARAMS}" CACHE STRING "")

libcxx/include/__config

@@ -14,6 +14,7 @@
 #include <__configuration/abi.h>
 #include <__configuration/availability.h>
 #include <__configuration/compiler.h>
+#include <__configuration/cxx03.h>
 #include <__configuration/platform.h>
 
 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
@@ -151,11 +152,6 @@ _LIBCPP_HARDENING_MODE_DEBUG
 #  define _LIBCPP_TOSTRING2(x) #x
 #  define _LIBCPP_TOSTRING(x) _LIBCPP_TOSTRING2(x)
 
-// NOLINTNEXTLINE(libcpp-cpp-version-check)
-#  if __cplusplus < 201103L
-#    define _LIBCPP_CXX03_LANG
-#  endif
-
 #  ifndef __has_constexpr_builtin
 #    define __has_constexpr_builtin(x) 0
 #  endif

libcxx/include/__configuration/cxx03.h

@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___CONFIGURATION_CXX03_H
+#define _LIBCPP___CONFIGURATION_CXX03_H
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+// NOLINTNEXTLINE(libcpp-cpp-version-check)
+#  if __cplusplus < 201103L
+#    define _LIBCPP_CXX03_LANG
+#  endif
+
+#endif // _LIBCPP___CONFIGURATION_CXX03_H

libcxx/include/__cxx03/__config

@@ -157,11 +157,6 @@ _LIBCPP_HARDENING_MODE_DEBUG
 #  define _LIBCPP_TOSTRING2(x) #x
 #  define _LIBCPP_TOSTRING(x) _LIBCPP_TOSTRING2(x)
 
-// NOLINTNEXTLINE(libcpp-cpp-version-check)
-#  if __cplusplus < 201103L
-#    define _LIBCPP_CXX03_LANG
-#  endif
-
 #  ifndef __has_constexpr_builtin
 #    define __has_constexpr_builtin(x) 0
 #  endif

libcxx/include/__flat_map/sorted_unique.h

@@ -9,11 +9,12 @@
 #ifndef _LIBCPP___FLAT_MAP_SORTED_UNIQUE_H
 #define _LIBCPP___FLAT_MAP_SORTED_UNIQUE_H
 
-#include <__config>
+#include <__configuration/cxx03.h>
 
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
+#if defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_USE_CXX03_HEADERS)
+#  include <__cxx03/locale.h>
+#else
+#  include <__config>
 
 #if _LIBCPP_STD_VER >= 23