gnulib: update to latest upstream revision.

* gnulib: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>

diff --git a/gnulib b/gnulib
index 9fc81090f6c5590bd1b0e0fa5087577a2ee43a3e..5191b3546cfb6c163228c23f214e325ddf60d46f 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 9fc81090f6c5590bd1b0e0fa5087577a2ee43a3e
+Subproject commit 5191b3546cfb6c163228c23f214e325ddf60d46f