[Bug gcov-profile/94570] -fprofile-dir is broken on Cygwin

[10walls at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94570

--- Comment #9 from jon_y <10walls at gmail dot com> ---
if defined(__MSDOS__) || (defined(_WIN32) && ! defined(__CYGWIN__) ||
defined(__OS2__)

I've tested the above and confirmed that coverage.ii does have the correct
separator after updating filenames.h.

Cygwin may define _WIN32 if win32api headers are included, but mingw will never
define __CYGWIN__.