[gcc(refs/users/kmatsui/heads/is_volatile)] libstdc++: use new built-in trait __is_volatile

[Ken Matsui <kmatsui@gcc.gnu.org>]

https://gcc.gnu.org/g:f6dc7dbf10d45628b163b1a8fde5e5655f4a4cfd

commit f6dc7dbf10d45628b163b1a8fde5e5655f4a4cfd
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Wed Mar 22 16:28:06 2023 -0700

    libstdc++: use new built-in trait __is_volatile
    
    This patch lets libstdc++ use new built-in trait __is_volatile.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_volatile): Use __is_volatile built-in
            trait.
            (is_volatile_v): Likewise.
    
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>

Diff:
---
 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..db74b884b35 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -773,6 +773,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public true_type { };
 
   /// is_volatile
+#if __has_builtin(__is_volatile)
+  template<typename _Tp>
+    struct is_volatile
+    : public __bool_constant<__is_volatile(_Tp)>
+    { };
+#else
   template<typename>
     struct is_volatile
     : public false_type { };
@@ -780,6 +786,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct is_volatile<_Tp volatile>
     : public true_type { };
+#endif
 
   /// is_trivial
   template<typename _Tp>
@@ -3214,10 +3221,16 @@ template <typename _Tp>
   inline constexpr bool is_const_v = false;
 template <typename _Tp>
   inline constexpr bool is_const_v<const _Tp> = true;
+
+#if __has_builtin(__is_volatile)
+template <typename _Tp>
+  inline constexpr bool is_volatile_v = __is_volatile(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_volatile_v = false;
 template <typename _Tp>
   inline constexpr bool is_volatile_v<volatile _Tp> = true;
+#endif
 
 template <typename _Tp>
   inline constexpr bool is_trivial_v = __is_trivial(_Tp);