[Bug libstdc++/104217] [12 Regression] gcc-12-20220123 failure to build on Cygwin due to lack of secure_getenv

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104217

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
so the cygwin libraries include secure_getenv but the header file defines it
only when __GNU_VISIBLE is true. Someone who knows cygwin headers can better
help here than me really. But I think libstdc++ checks only if secure_getenv is
in the library and not the header .... Having it check the include might be
useful too.