[committed] libstdc++: Use variable template to fix -fconcepts-ts error [PR113366]

[committed] libstdc++: Use variable template to fix -fconcepts-ts error [PR113366]

[Jonathan Wakely]

Tested x86_64-linux. Pushed to trunk.

-- >8 --

There's an error for -fconcepts-ts due to using a concept where a bool
NTTP is required, which is fixed by using the vraiable template that
already exists in the class scope.

This doesn't fix the problem with -fconcepts-ts as changes to the
placement of attributes is also needed.

libstdc++-v3/ChangeLog:

	PR testsuite/113366
	* include/std/format (basic_format_arg): Use __formattable
	variable template instead of __format::__formattable_with
	concept.
---
 libstdc++-v3/include/std/format | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 540f8b805f8..efc4a17ba36 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3189,8 +3189,7 @@ namespace __format
 	// Format as const if possible, to reduce instantiations.
 	template<typename _Tp>
 	  using __maybe_const_t
-	    = __conditional_t<__format::__formattable_with<_Tp, _Context>,
-			      const _Tp, _Tp>;
+	    = __conditional_t<__formattable<_Tp>, const _Tp, _Tp>;
 
 	template<typename _Tq>
 	  static void
@@ -3208,7 +3207,7 @@ namespace __format
 	  explicit
 	  handle(_Tp& __val) noexcept
 	  {
-	    if constexpr (!__format::__formattable_with<const _Tp, _Context>)
+	    if constexpr (!__formattable<const _Tp>)
 	      static_assert(!is_const_v<_Tp>, "std::format argument must be "
 					      "non-const for this type");
 
-- 
2.43.0