Update to newest gnulib.

diff --git a/gnulib b/gnulib
index a18f7ce3c0aa760c33d46bbeb8e5b3a14cf24984..91584ed612fa26a505c8fc4c7f6fb19f7413795d 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit a18f7ce3c0aa760c33d46bbeb8e5b3a14cf24984
+Subproject commit 91584ed612fa26a505c8fc4c7f6fb19f7413795d