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: NEric Blake <eblake@redhat.com>

.gnulib @ 9d5efe7d

-Subproject commit d55899fd2c5794ac85ecb14d5e2f646a89e4b4dd
+Subproject commit 9d5efe7d61e1d96a6d7c97ffa4d21c5e33e9bd30