libstdc++: Optimize is_compound trait performance

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

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_compound): Use __is_arithmetic
	built-in trait.
	(is_compound_v): Use is_fundamental_v instead.

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

libstdc++-v3/include/std/type_traits

@@ -702,9 +702,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
   /// is_compound
+#if __has_builtin(__is_arithmetic)
+  template<typename _Tp>
+    struct is_compound
+    : public __bool_constant<!(__is_arithmetic(_Tp)
+                             || is_void<_Tp>::value
+                             || is_null_pointer<_Tp>::value)>
+    { };
+#else
   template<typename _Tp>
     struct is_compound
     : public __not_<is_fundamental<_Tp>>::type { };
+#endif
 
   /// @cond undocumented
   template<typename _Tp>
@@ -3234,7 +3243,7 @@ template <typename _Tp>
 template <typename _Tp>
   inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
 template <typename _Tp>
-  inline constexpr bool is_compound_v = is_compound<_Tp>::value;
+  inline constexpr bool is_compound_v = !is_fundamental_v<_Tp>;
 template <typename _Tp>
   inline constexpr bool is_member_pointer_v = is_member_pointer<_Tp>::value;
 template <typename _Tp>