Update to the newest gnulib.

diff --git a/gnulib b/gnulib
index bbf0d3fdf25e8f85c7751ac0ee90a0f50a0f054d..4ca39f72e42d04184a97ac28d284a3039723e76e 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit bbf0d3fdf25e8f85c7751ac0ee90a0f50a0f054d
+Subproject commit 4ca39f72e42d04184a97ac28d284a3039723e76e