[Bug libstdc++/51785] gets not anymore declared

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #29 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to andyg1001 from comment #28)
> Erm, am I the first to notice that this "solution" is broken?

No, see https://gcc.gnu.org/ml/libstdc++/2016-09/msg00228.html

> The os_defines.h include that undefines _GLIBCXX_HAVE_GETS is included
> before _GLIBCXX_HAVE_GETS is (re)defined inside c++config.h.
> 
> Therefore, _GLIBCXX_HAVE_GETS is still defined when we get to <cstdio>.
>
> Seems still to be broken even in trunk.

PR 77795 improved things. What's still broken? We need a testcase showing the
problem.