[PATCH v2 4/7] libstdc++: use new built-in trait __is_function for std::is_function

[Ken Matsui via Gcc-patches]

This patch gets std::is_function to dispatch to new built-in trait
__is_function.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_function): Use __is_function built-in
        trait.

Signed-off-by: Ken Matsui <kmat...@cs.washington.edu>
---
 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 58a732735c8..9eafd6b16f2 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -594,6 +594,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
   /// is_function
+#if __has_builtin(__is_function)
+  template<typename _Tp>
+    struct is_function
+    : public __bool_constant<__is_function(_Tp)>
+    { };
+#else
   template<typename _Tp>
     struct is_function
     : public __bool_constant<!is_const<const _Tp>::value> { };
@@ -605,6 +611,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct is_function<_Tp&&>
     : public false_type { };
+#endif
 
 #define __cpp_lib_is_null_pointer 201309L
 
-- 
2.40.0