[gcc r14-11193] libstdc++: Use feature test macro for pmr::polymorphic_allocator<>

[Jonathan Wakely]

https://gcc.gnu.org/g:a4c0f16f048b64c1ab3b2521e3a1595afc64462b

commit r14-11193-ga4c0f16f048b64c1ab3b2521e3a1595afc64462b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Dec 10 14:35:07 2024 +0000

    libstdc++: Use feature test macro for pmr::polymorphic_allocator<>
    
    Check the __glibcxx_polymorphic_allocator macro instead of just checking
    whether __cplusplus > 201703L.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/memory_resource.h (polymoprhic_allocator): Use
            feature test macro for P0339R6 features.
    
    (cherry picked from commit b26d92f4f71594206385d6f645ff626c0bf9b59c)

Diff:
---
 libstdc++-v3/include/bits/memory_resource.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/memory_resource.h b/libstdc++-v3/include/bits/memory_resource.h
index db515fb30ef9..9bfeaedf078d 100644
--- a/libstdc++-v3/include/bits/memory_resource.h
+++ b/libstdc++-v3/include/bits/memory_resource.h
@@ -168,7 +168,7 @@ namespace pmr
       __attribute__((__nonnull__))
       { _M_resource->deallocate(__p, __n * sizeof(_Tp), alignof(_Tp)); }
 
-#if __cplusplus > 201703L
+#ifdef __glibcxx_polymorphic_allocator // >= C++20
       [[nodiscard]] void*
       allocate_bytes(size_t __nbytes,
 		     size_t __alignment = alignof(max_align_t))
@@ -218,9 +218,9 @@ namespace pmr
 	  __p->~_Up();
 	  deallocate_object(__p);
 	}
-#endif // C++2a
+#endif // C++20
 
-#if ! __glibcxx_make_obj_using_allocator
+#if ! __glibcxx_make_obj_using_allocator // >= C++20
       template<typename _Tp1, typename... _Args>
 	__attribute__((__nonnull__))
 	typename __not_pair<_Tp1>::type
@@ -336,7 +336,7 @@ namespace pmr
 #endif
 
     private:
-#if ! __glibcxx_make_obj_using_allocator
+#if ! __glibcxx_make_obj_using_allocator // >= C++20
       using __uses_alloc1_ = __uses_alloc1<polymorphic_allocator>;
       using __uses_alloc2_ = __uses_alloc2<polymorphic_allocator>;