[Bug bootstrap/67546] bootstrap broken on x86_64-w64-mingw32, error: '::unsetenv' has not been declared in gcc.c

[rainer@emrich-ebersheim.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67546

--- Comment #2 from Rainer Emrich <rainer@emrich-ebersheim.de> ---
(In reply to Kai Tietz from comment #1)
> I added to mingw-w64's libwinpthread a work-a-round for this sloopy code in
> libgomp.  Nevertheless issue should be fixed IMO in libgomp, too

Wrong PR, this belongs to PR67141.