libstdc++: Optimize is_fundamental trait performance

This patch optimizes the performance of the is_fundamental trait by
dispatching to the new __is_arithmetic built-in trait.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_fundamental_v): Use __is_arithmetic
	built-in trait.
	(is_fundamental): Likewise. Optimize the original implementation.

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>

libstdc++-v3/include/std/type_traits

@@ -668,11 +668,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   /// is_fundamental
+#if __has_builtin(__is_arithmetic)
+  template<typename _Tp>
+    struct is_fundamental
+    : public __bool_constant<__is_arithmetic(_Tp)
+                             || is_void<_Tp>::value
+                             || is_null_pointer<_Tp>::value>
+    { };
+#else
   template<typename _Tp>
     struct is_fundamental
-    : public __or_<is_arithmetic<_Tp>, is_void<_Tp>,
-		   is_null_pointer<_Tp>>::type
+    : public __bool_constant<is_arithmetic<_Tp>::value
+                             || is_void<_Tp>::value
+                             || is_null_pointer<_Tp>::value>
     { };
+#endif
 
   /// is_object
   template<typename _Tp>
@@ -3209,13 +3219,16 @@ template <typename _Tp>
 #if __has_builtin(__is_arithmetic)
 template <typename _Tp>
   inline constexpr bool is_arithmetic_v = __is_arithmetic(_Tp);
+template <typename _Tp>
+  inline constexpr bool is_fundamental_v
+    = __is_arithmetic(_Tp) || is_void_v<_Tp> || is_null_pointer_v<_Tp>;
 #else
 template <typename _Tp>
   inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
-#endif
-
 template <typename _Tp>
   inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_object_v = is_object<_Tp>::value;
 template <typename _Tp>