[gcc(refs/users/kmatsui/heads/is_scalar)] libstdc++: use new built-in trait __is_scalar for std::is_scalar

[gcc(refs/users/kmatsui/heads/is_scalar)] libstdc++: use new built-in trait __is_scalar for std::is_scalar

[Ken Matsui]

https://gcc.gnu.org/g:4f64023297b188a595780423cd4daad3e72b7ff9

commit 4f64023297b188a595780423cd4daad3e72b7ff9
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Mon Jul 3 01:56:19 2023 -0700

    libstdc++: use new built-in trait __is_scalar for std::is_scalar
    
    This patch gets std::is_scalar to dispatch to new built-in trait
    __is_scalar.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_scalar): Use __is_scalar built-in
            trait.
            (is_scalar_v): Likewise.
    
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>

Diff:
---
 libstdc++-v3/include/std/type_traits | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 0e7a9c9c7f3..bc90b2c61ca 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -678,11 +678,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct is_member_pointer;
 
   /// is_scalar
+#if __has_builtin(__is_scalar)
+  template<typename _Tp>
+    struct is_scalar
+    : public __bool_constant<__is_scalar(_Tp)>
+    { };
+#else
   template<typename _Tp>
     struct is_scalar
     : public __or_<is_arithmetic<_Tp>, is_enum<_Tp>, is_pointer<_Tp>,
                    is_member_pointer<_Tp>, is_null_pointer<_Tp>>::type
     { };
+#endif
 
   /// is_compound
   template<typename _Tp>
@@ -3204,8 +3211,15 @@ template <typename _Tp>
   inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
 template <typename _Tp>
   inline constexpr bool is_object_v = is_object<_Tp>::value;
+
+#if __has_builtin(__is_scalar)
+template <typename _Tp>
+  inline constexpr bool is_scalar_v = __is_scalar(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_compound_v = is_compound<_Tp>::value;
 template <typename _Tp>