maint: update to latest gnulib

maint: update to latest gnulib

When run under an environment that inherits an ignored SIGPIPE
(hello, annoying buildbots), a syntax-check was producing quite
a bit of noise, such as:

> prohibit_argmatch_without_use
> grep: write error
> grep: write error
> /bin/sed: couldn't write 25 items to stdout: Broken pipe
> sed: couldn't write 1 item to stdout: Broken pipe
> 0.46 prohibit_argmatch_without_use

This has been fixed upstream in gnulib.  There are several other
portability improvements in our regular submodule update.

* .gnulib: Update to latest, in part for quieter syntax-check.

Signed-off-by: Eric Blake <eblake@redhat.com>