Update to the newest gnulib.

diff --git a/gnulib b/gnulib
index 64042bb91aea5f854ca8a8938e2b3f7d1935e4f1..f4c40c2d6aabef8e587176bbf5226c8bc6649574 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 64042bb91aea5f854ca8a8938e2b3f7d1935e4f1
+Subproject commit f4c40c2d6aabef8e587176bbf5226c8bc6649574