Update to newest gnulib.

diff --git a/gnulib b/gnulib
index 17c967e57bf89d4c6fc0e94453814cf6852e39e2..a18f7ce3c0aa760c33d46bbeb8e5b3a14cf24984 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 17c967e57bf89d4c6fc0e94453814cf6852e39e2
+Subproject commit a18f7ce3c0aa760c33d46bbeb8e5b3a14cf24984