build: update gnulib submodule to latest, and adapt

build: update gnulib submodule to latest, and adapt

* cfg.mk: Update to use new _sc_search_regexp interface.  Run this:
perl -pi -e 's/\b_prohibit_regexp\b/_sc_search_regexp/;'
-e 's/\bmsg=/halt=/; s/\bre=/prohibit=/;' cfg.mk
and then adjust backslashes so they still line up.
* cfg.mk (local-checks-to-skip): Add new sc_texinfo_acronym, to skip it.
* msdos/tailor.c (fcalloc): Mark a diagnostic for translation, to
placate stricter syntax-check, even though no one uses this file.