[PATCH v2 2/2] libstdc++: use new built-in trait __is_unsigned

[Ken Matsui]

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.
---
 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 2bd607a8b8f..8d5a05cd0a6 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&&>
-- 
2.40.0