Update to the newest gnulib.

diff --git a/gnulib b/gnulib
index 4a1b37a5717ddccd31c3516cfb7dba0b9eab2252..c0e56f571eca7b84b629fce2b9b05be5c4c26137 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 4a1b37a5717ddccd31c3516cfb7dba0b9eab2252
+Subproject commit c0e56f571eca7b84b629fce2b9b05be5c4c26137