maint: update to latest gnulib

Since we haven't quite frozen yet, it's time to pick up some
gnulib fixes.  I know at least cygwin benefits from this update.

* .gnulib: Update to latest, in part for cygwin compilation.
Signed-off-by: NEric Blake <eblake@redhat.com>

.gnulib @ 8f742586

-Subproject commit 4a5ee89c8a8be7350a8fd8ca1bacb196a190e492
+Subproject commit 8f7425866463f994538584d1dd7211603b8b0550