[gcc r13-1286] libstdc++: Simplify fs::path construction using variable template

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:6177f60d914abcb8520b87ae62658e70a7c13759

commit r13-1286-g6177f60d914abcb8520b87ae62658e70a7c13759
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jun 23 18:39:50 2022 +0100

    libstdc++: Simplify fs::path construction using variable template
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/fs_path.h (__is_path_iter_src): Replace class
            template with variable template.

Diff:
---
 libstdc++-v3/include/bits/fs_path.h | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index d6202fd275a..6e7b366d104 100644
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -102,19 +102,16 @@ namespace __detail
 #endif
 
   template<typename _Iter_traits, typename = void>
-    struct __is_path_iter_src
-    : false_type
-    { };
+    inline constexpr bool __is_path_iter_src = false;
 
   template<typename _Iter_traits>
-    struct __is_path_iter_src<_Iter_traits,
-			      void_t<typename _Iter_traits::value_type>>
-    : bool_constant<__is_encoded_char<typename _Iter_traits::value_type>>
-    { };
+    inline constexpr bool
+    __is_path_iter_src<_Iter_traits, void_t<typename _Iter_traits::value_type>>
+      = __is_encoded_char<typename _Iter_traits::value_type>;
 
   template<typename _Source>
     inline constexpr bool __is_path_src
-      = __is_path_iter_src<iterator_traits<decay_t<_Source>>>::value;
+      = __is_path_iter_src<iterator_traits<decay_t<_Source>>>;
 
   template<>
     inline constexpr bool __is_path_src<path> = false;
@@ -150,7 +147,7 @@ namespace __detail
 
   // SFINAE constraint for InputIterator parameters as required by [fs.req].
   template<typename _Iter, typename _Tr = __safe_iterator_traits<_Iter>>
-    using _Path2 = enable_if_t<__is_path_iter_src<_Tr>::value, path>;
+    using _Path2 = enable_if_t<__is_path_iter_src<_Tr>, path>;
 
 #if __cpp_lib_concepts
   template<typename _Iter>