[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

--- Comment #21 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #20)
> Another option would be to implement clang's using_if_exists attribute, so
> that we'd do:

See #105584 (not auto-linking intentionally because I don't want to notify the
reporter).