build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 7347caeb9d902d3fca2c11f69a55a3e578d93bfe..2ef6006ffc4080cf8c0c1f4d4deeb4c357d7a695 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 7347caeb9d902d3fca2c11f69a55a3e578d93bfe
+Subproject commit 2ef6006ffc4080cf8c0c1f4d4deeb4c357d7a695