build: update from gnulib (hash module updates; maint.mk tweak)

* gnulib: Update submodule to latest.

diff --git a/gnulib b/gnulib
index facd2482db60c9e08f60ecd6f004940393e1630a..12f78b4faa14cd2da952f865979843dee79fcf93 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit facd2482db60c9e08f60ecd6f004940393e1630a
+Subproject commit 12f78b4faa14cd2da952f865979843dee79fcf93