build: fix gnulib build for mingw

Pavel flagged a build regression under mingw, and traced it to a
recent flaw in gnulib for working around nl_langinfo. This picks
up the fix.

* gnulib: Update to latest, for mingw build fixes.
Signed-off-by: NEric Blake <eblake@redhat.com>

.gnulib @ 2d280742

-Subproject commit 9d5efe7d61e1d96a6d7c97ffa4d21c5e33e9bd30
+Subproject commit 2d280742a9e30088aa169f53353765d5daafe4c0