[PATCH] libstdc++: use new built-in trait __remove_pointer

[Ken Matsui via Gcc-patches]

libstdc++-v3/ChangeLog:

* include/std/type_traits (is_reference): Use __remove_pointer built-in trait.

---
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index 2bd607a8b8f..cba98091aad 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2025,17 +2025,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION

   template<typename _Tp, typename>
     struct __remove_pointer_helper
-    { typedef _Tp     type; };
+    { using type = _Tp; };

   template<typename _Tp, typename _Up>
     struct __remove_pointer_helper<_Tp, _Up*>
-    { typedef _Up     type; };
+    { using type = _Up; };

   /// remove_pointer
+#if __has_builtin(__remove_pointer)
+  template<typename _Tp>
+    struct remove_pointer
+    { using type = __remove_pointer(_Tp); };
+#else
   template<typename _Tp>
     struct remove_pointer
     : public __remove_pointer_helper<_Tp, __remove_cv_t<_Tp>>
     { };
+#endif

   template<typename _Tp, typename = void>
     struct __add_pointer_helper