[PATCH] libstdc++: Define _GLIBCXX_HAS_BUILTIN_TRAIT

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

This patch defines _GLIBCXX_HAS_BUILTIN_TRAIT, which will be used as a
flag to toggle built-in traits in the type_traits header. Through this
macro function and _GLIBCXX_NO_BUILTIN_TRAITS macro, we can switch the
use of built-in traits without needing to modify the source code.

libstdc++-v3/ChangeLog:

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

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
---
 libstdc++-v3/include/bits/c++config | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index dd47f274d5f..de13f61db71 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -854,7 +854,11 @@ namespace __gnu_cxx
 # define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
 #endif
 
-#undef _GLIBCXX_HAS_BUILTIN
+// Returns true if _GLIBCXX_NO_BUILTIN_TRAITS is not defined and the compiler
+// has a corresponding built-in type trait. _GLIBCXX_NO_BUILTIN_TRAITS is
+// defined to disable the use of built-in traits.
+#define _GLIBCXX_HAS_BUILTIN_TRAIT(BT)  \
+  (!defined(_GLIBCXX_NO_BUILTIN_TRAITS) && _GLIBCXX_HAS_BUILTIN(BT))
 
 // Mark code that should be ignored by the compiler, but seen by Doxygen.
 #define _GLIBCXX_DOXYGEN_ONLY(X)
-- 
2.41.0