[PATCH v4 2/2] libstdc++: use new built-in trait __is_unsigned

[Ken Matsui via Gcc-patches]

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

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_unsigned): Use __is_unsigned built-in
        trait.
        (is_unsigned_v): Likewise.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/std/type_traits | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 0e7a9c9c7f3..7eeb0da7a27 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -884,10 +884,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
   /// is_unsigned
+#if __has_builtin(__is_unsigned)
+  template<typename _Tp>
+    struct is_unsigned
+    : public __bool_constant<__is_unsigned(_Tp)>
+    { };
+#else
   template<typename _Tp>
     struct is_unsigned
     : public __and_<is_arithmetic<_Tp>, __not_<is_signed<_Tp>>>::type
     { };
+#endif
 
   /// @cond undocumented
   template<typename _Tp, typename _Up = _Tp&&>
@@ -3242,8 +3249,14 @@ template <typename _Tp>
 
 template <typename _Tp>
   inline constexpr bool is_signed_v = is_signed<_Tp>::value;
+
+#if __has_builtin(__is_unsigned)
+template <typename _Tp>
+  inline constexpr bool is_unsigned_v = __is_unsigned(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_unsigned_v = is_unsigned<_Tp>::value;
+#endif
 
 template <typename _Tp, typename... _Args>
   inline constexpr bool is_constructible_v = __is_constructible(_Tp, _Args...);
-- 
2.41.0