build: update gnulib submodule to latest

* cfg.mk (local-checks-to-skip): Disable sc_prohibit_hash_without_use
for now, since it fails with a false-positive match.

.gnulib @ 2709233e

-Subproject commit 11fbc57405a118e6ec9a3ebc19bbf5ececdae4d6
+Subproject commit 2709233ead439b582d82af48bd25e709378cda44

cfg.mk

@@ -42,6 +42,7 @@ local-checks-to-skip =			\
   sc_obsolete_symbols			\
   sc_prohibit_S_IS_definition		\
   sc_prohibit_atoi_atof			\
+  sc_prohibit_hash_without_use		\
   sc_prohibit_jm_in_m4			\
   sc_prohibit_quote_without_use		\
   sc_prohibit_quotearg_without_use	\