[Bug libfortran/66936] io/unix.c gratuitously uses S_IRWXG and S_IRWXO on the basis that umask() is available

[keith.marshall at mailinator dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66936

--- Comment #18 from Keith Marshall <keith.marshall at mailinator dot com> ---
(In reply to Francois-Xavier Coudert from comment #17)
> Given the history and reasons, I've committed the patch to restore build on
> mingw32. Marking as fixed on trunk.

Thanks.  Looks like a cleaner way to achieve the same effect as my own Q&D
hack.  Reverted mine, and applied this to my 4.9.3 tree; can confirm that it
now builds successfully for mingw32, (as crossed-native build from GNU/Linux;
still can't build 5.x, but that's an entirely different issue).

I haven't written any Fortran code in near 15 years, and no longer run Windows
myself anyway, so haven't tested usability; let's push it out there, and see if
anyone in the MinGW.org community can identify any consequent problems.