[PATCH v2] libstdc++: Define _GLIBCXX_HAS_BUILTIN_TRAIT

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

This patch defines _GLIBCXX_HAS_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_NO_BUILTIN_TRAITS macro, without needing to modify the
source code.

libstdc++-v3/ChangeLog:

	* include/bits/c++config (_GLIBCXX_HAS_BUILTIN_TRAIT): Define.
	(_GLIBCXX_HAS_BUILTIN): Keep defined.

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
---
 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 dd47f274d5f..984985d6fff 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_NO_BUILTIN_TRAITS is not defined and the compiler
+// has a corresponding built-in type trait, 0 otherwise.
+// _GLIBCXX_NO_BUILTIN_TRAITS can be defined to disable the use of built-in
+// traits.
+#ifndef _GLIBCXX_NO_BUILTIN_TRAITS
+# define _GLIBCXX_HAS_BUILTIN_TRAIT(BT) _GLIBCXX_HAS_BUILTIN(BT)
+#else
+# define _GLIBCXX_HAS_BUILTIN_TRAIT(BT) 0
+#endif
 
 // Mark code that should be ignored by the compiler, but seen by Doxygen.
 #define _GLIBCXX_DOXYGEN_ONLY(X)
-- 
2.41.0