Update to the newest gnulib.

diff --git a/gnulib b/gnulib
index 6ef3d783333346333f35bb181ba90f5bc46c0b29..6542d39be48065193e9c64dcb6eb0d854a1242dc 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 6ef3d783333346333f35bb181ba90f5bc46c0b29
+Subproject commit 6542d39be48065193e9c64dcb6eb0d854a1242dc