[Bug c/71255] Implement #pragma may_alias

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71255

--- Comment #25 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #23)
> (In reply to Florian Weimer from comment #22)
> > (In reply to Marek Polacek from comment #21)
> > > The testcase in Comment 14 should now compile fine.
> > 
> > What's the best way to detect that a compiler has this fix?  We cannot use a
> > configure check.  Is there anything better than looking at __GNUC__?  Are
> > you going to backport this fix?  Thanks.
> 
> It seems a good motivation to add the __has_feature(pragma_may_alias)

Not really.  The expectation is that after these bug fixes, we won't need the
pragma.