[PATCH 2/2] libstdc++: use new built-in trait __is_volatile

[Ken Matsui via Gcc-patches]

This patch lets libstdc++ use new built-in trait __is_volatile.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_volatile): Use __is_volatile built-in
        trait.
---
 libstdc++-v3/include/std/type_traits | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 2bd607a8b8f..c50c8dba396 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -773,6 +773,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public true_type { };
 
   /// is_volatile
+#if __has_builtin(__is_volatile)
+  template<typename _Tp>
+    struct is_volatile
+    : public __bool_constant<__is_volatile(_Tp)>
+    { };
+#else
   template<typename>
     struct is_volatile
     : public false_type { };
@@ -780,6 +786,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct is_volatile<_Tp volatile>
     : public true_type { };
+#endif
 
   /// is_trivial
   template<typename _Tp>
-- 
2.40.0