[gcc(refs/users/kmatsui/heads/use-is_enum)] libstdc++: use __is_enum built-in trait

[gcc(refs/users/kmatsui/heads/use-is_enum)] libstdc++: use __is_enum built-in trait

[Ken Matsui]

https://gcc.gnu.org/g:24cdd67a945c6fdb42269674fe8a792432508f0f

commit 24cdd67a945c6fdb42269674fe8a792432508f0f
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Sun Jul 2 18:12:30 2023 -0700

    libstdc++: use __is_enum built-in trait
    
    This patch replaces is_enum<T>::value with __is_enum built-in trait in
    the type_traits header.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (__make_unsigned_selector): Use
            __is_enum built-in trait.
            (__make_signed_selector): Likewise.
            (__underlying_type_impl): Likewise.
    
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>

Diff:
---
 libstdc++-v3/include/std/type_traits | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 0e7a9c9c7f3..9f086992ebc 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1740,7 +1740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Select between integral and enum: not possible to be both.
   template<typename _Tp,
 	   bool _IsInt = is_integral<_Tp>::value,
-	   bool _IsEnum = is_enum<_Tp>::value>
+	   bool _IsEnum = __is_enum(_Tp)>
     class __make_unsigned_selector;
 
   template<typename _Tp>
@@ -1900,7 +1900,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Select between integral and enum: not possible to be both.
   template<typename _Tp,
 	   bool _IsInt = is_integral<_Tp>::value,
-	   bool _IsEnum = is_enum<_Tp>::value>
+	   bool _IsEnum = __is_enum(_Tp)>
     class __make_signed_selector;
 
   template<typename _Tp>
@@ -2353,7 +2353,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct __common_type_fold<_CTp, _Rp, void>
     { };
 
-  template<typename _Tp, bool = is_enum<_Tp>::value>
+  template<typename _Tp, bool = __is_enum(_Tp)>
     struct __underlying_type_impl
     {
       using type = __underlying_type(_Tp);