[gcc(refs/users/aoliva/heads/testme)] enable __GXX_WEAK__ when using weak for one-only

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:79ccdb557f8207dfebc9a9fb541193deeec559f0

commit 79ccdb557f8207dfebc9a9fb541193deeec559f0
Author: Alexandre Oliva <oliva@gnu.org>
Date:   Fri Nov 25 02:06:46 2022 -0300

    enable __GXX_WEAK__ when using weak for one-only

Diff:
---
 gcc/c-family/c-cppbuiltin.cc | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index 333f3e138d6..15ef47c0c04 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -939,7 +939,15 @@ c_cpp_builtins (cpp_reader *pfile)
 
   if (c_dialect_cxx ())
     {
-      if (flag_weak && SUPPORTS_ONE_ONLY)
+      /* __GXX_WEAK__'s name is misleading, the documentation says it
+	 tests for one-only spuport, but SUPPORTS_ONE_ONLY is also
+	 slightly misleading, because weak symbols can be used for
+	 one-only support even if !SUPPORtS_ONE_ONLY.  Here we
+	 approximate the supprots_one_only() test that may clear
+	 flag_weak, but we use the flag_weak result instead of
+	 TARGET_SUPPORTS_WEAK, because the user may have disabled weak
+	 symbols with -fno-weak.  */
+      if (flag_weak || SUPPORTS_ONE_ONLY)
 	cpp_define (pfile, "__GXX_WEAK__=1");
       else
 	cpp_define (pfile, "__GXX_WEAK__=0");