[gcc r14-3844] libstdc++: Define _GLIBCXX_USE_BUILTIN_TRAIT

[Ken Matsui <kmatsui@gcc.gnu.org>]

https://gcc.gnu.org/g:286655d04678cb61dee9cac43b139571247c4ad1

commit r14-3844-g286655d04678cb61dee9cac43b139571247c4ad1
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Tue Jul 18 15:24:50 2023 -0700

    libstdc++: Define _GLIBCXX_USE_BUILTIN_TRAIT
    
    This patch defines _GLIBCXX_USE_BUILTIN_TRAIT macro, which will be used
    as a flag to toggle the use of built-in traits in the type_traits header
    through _GLIBCXX_DO_NOT_USE_BUILTIN_TRAITS macro, without needing to modify
    the source code.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/c++config (_GLIBCXX_HAS_BUILTIN): Do not undef.
            (_GLIBCXX_USE_BUILTIN_TRAIT): Define.
    
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
    Reviewed-by: Patrick Palka <ppalka@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/c++config | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 0a41cdd29a9a..410c136e1b11 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -854,7 +854,15 @@ namespace __gnu_cxx
 # define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
 #endif
 
-#undef _GLIBCXX_HAS_BUILTIN
+// Returns 1 if _GLIBCXX_DO_NOT_USE_BUILTIN_TRAITS is not defined and the
+// compiler has a corresponding built-in type trait, 0 otherwise.
+// _GLIBCXX_DO_NOT_USE_BUILTIN_TRAITS can be defined to disable the use of
+// built-in traits.
+#ifndef _GLIBCXX_DO_NOT_USE_BUILTIN_TRAITS
+# define _GLIBCXX_USE_BUILTIN_TRAIT(BT) _GLIBCXX_HAS_BUILTIN(BT)
+#else
+# define _GLIBCXX_USE_BUILTIN_TRAIT(BT) 0
+#endif
 
 // Mark code that should be ignored by the compiler, but seen by Doxygen.
 #define _GLIBCXX_DOXYGEN_ONLY(X)