build: update gnulib submodule to latest

* .gnulib: This fixes a warning in test-gettimeofday.c,
seen via "make check".  Reported by Daniel Veillard.

diff --git a/.gnulib b/.gnulib
index 9d0ad652de159d08e5f679842f8a2a5658196361..11fbc57405a118e6ec9a3ebc19bbf5ececdae4d6 160000 (submodule)
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit 9d0ad652de159d08e5f679842f8a2a5658196361
+Subproject commit 11fbc57405a118e6ec9a3ebc19bbf5ececdae4d6