Gnulib recently patched gcc warning detection so that it does
not treat things like -Wno-unused-command-line-argument as
supported in gcc (treating it as supported merely resulted in
extra verbosity when an actual compile error occurred).  It
has also improved bootstrap to work with less hassle on OpenBSD.

* .gnulib: Update to latest, in part for bootstrap and warnings
improvements.
* bootstrap: Resync from gnulib.
Signed-off-by: NEric Blake <eblake@redhat.com>