[Bug libstdc++/78905] Add a macro to determine that the <regex> library is implemented

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78905

Eric Gallager <egall at gwmail dot gwu.edu> changed:

           What    |Removed                     |Added
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                 CC|                            |egall at gwmail dot gwu.edu

--- Comment #10 from Eric Gallager <egall at gwmail dot gwu.edu> ---
(In reply to Jonathan Wakely from comment #8)
> (In reply to Matt Clarkson from comment #2)
> > Because wehen I compile with clang against the libstdc++ the problem will
> > still occur and __GNUC__ will not be defined.
> 
> N.B. Clang does define __GNUC__ but it always defines it to 4 (and defines
> __GNUC_MINOR__ to 1 and __GNUC_PATCHLEVEL__ to 2, because it identifies as
> GCC 4.1.2, the last release Apple shipped for their OS).

__GNUC_MINOR__ and __GNUC_PATCHLEVEL__ values are swapped with each other
there; last release Apple shipped for their OS was 4.2.1, not 4.1.2