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 --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 0a41cdd29a9a232b3a2fe82644758aef75b87c5c..410c136e1b11c5bc620406f7c1bf83ae5124c31d 100644 (file)
--- 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)