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

["keith.marshall at mailinator dot com" <gcc-bugzilla@gcc.gnu.org>]

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

            Bug ID: 66936
           Summary: io/unix.c gratuitously uses S_IRWXG and S_IRWXO on the
                    basis that mkstemp() is available
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: keith.marshall at mailinator dot com
  Target Milestone: ---

Created attachment 36013
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36013&action=edit
Kludge to work around issue for mingw32

When building GCC, with FORTRAN language support, for mingw32 with the
mingwrt-3.21+ runtime library from MinGW.org installed, the build fails in
libgfortran/io/unix.c, because the tempfile_open() function gratuitously
assumes that, if HAVE_MKSTEMP is defined, then it must invoke:

  mode_mask = umask (S_IXUSR | S_IRWXG | S_IRWXO);

regardless of whether or not those access mode flags are defined.  Of course,
the assumption is invalid: while S_IXUSR may have some semblance of meaning on
a windows host, and is defined, S_IRWXG and S_IRWXO are meaningless, and are
not.

Now, I can kludge around this, with the attached patch, but I suspect that it
doesn't represent a true solution.