build: update gnulib

Picks up fixes for gethostname compilation problems on mingw.

* .gnulib: Update to latest.
* build-aux/.gitignore: Regenerate.
* cfg.mk (local-checks-to-skip): Avoid new test not relevent to
libvirt.

build-aux/.gitignore

@@ -6,6 +6,7 @@
 /useless-if-before-free
 /vc-list-files
 arg-nonnull.h
+c++defs.h
 config.rpath
 gitlog-to-changelog
 mkinstalldirs

cfg.mk

@@ -51,6 +51,7 @@ local-checks-to-skip =			\
   sc_space_tab				\
   sc_sun_os_names			\
   sc_system_h_headers			\
+  sc_texinfo_acronym			\
   sc_tight_scope			\
   sc_two_space_separator_in_usage	\
   sc_error_message_uppercase		\