[Bug libstdc++/93469] memory header fails to compile with _XOPEN_SOURCE macro defined and -std=c++2a option specified

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93469

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://github.com/iains/gc
                   |                            |c-15-branch/issues/4

--- Comment #20 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Another option would be to implement clang's using_if_exists attribute, so that
we'd do:

#include <stdlib.h>
namespace std
{
using ::aligned_alloc __attribute__((__using_if_exists__));
}

and this would not declare anything if ::aligned_alloc hasn't been declared by
stdlib.h

This would get rid of a LOT of configury checks.