Update to newest gnulib.

diff --git a/gnulib b/gnulib
index 0f3906631fa19caed9321cab02e2f4ba0a3bde72..6642aeb47aee3d82978a27497dc9ca57058c66b4 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 0f3906631fa19caed9321cab02e2f4ba0a3bde72
+Subproject commit 6642aeb47aee3d82978a27497dc9ca57058c66b4