[gcc r14-946] libstdc++: Add system_header pragma to <bits/c++config.h>

[gcc r14-946] libstdc++: Add system_header pragma to <bits/c++config.h>

[Jonathan Wakely]

https://gcc.gnu.org/g:98827c53ed38886795b1f479c1d997fd89011c38

commit r14-946-g98827c53ed38886795b1f479c1d997fd89011c38
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed May 17 13:47:54 2023 +0100

    libstdc++: Add system_header pragma to <bits/c++config.h>
    
    Without this change many tests that depend on an effective-target will
    fail when compiled with -pedantic -std=c++98. This happens because the
    preprocessor check done by v3_check_preprocessor_condition uses -Werror
    and includes <bits/c++config.h> directly (rather than via another header
    like <string>). If <bits/c++config.h> is not a system header then this
    pedwarn is not suppressed, and the effective-target check fails:
    
    bits/c++config.h:220: error: anonymous variadic macros were introduced in C++11 [-Werror=variadic-macros]
    cc1plus: all warnings being treated as errors
    compiler exited with status 1
    UNSUPPORTED: 18_support/headers/limits/synopsis.cc
    
    We could consider also changing proc v3_check_preprocessor_condition so
    that it includes a real header, rather than just <bits/c++config.h>, but
    that's not necessary for now.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/c++config: Add system_header pragma.

Diff:
---
 libstdc++-v3/include/bits/c++config | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 13892787e09..009a017b048 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -30,6 +30,8 @@
 #ifndef _GLIBCXX_CXX_CONFIG_H
 #define _GLIBCXX_CXX_CONFIG_H 1
 
+#pragma GCC system_header
+
 // The major release number for the GCC release the C++ library belongs to.
 #define _GLIBCXX_RELEASE