maint: update gnulib to latest

* gnulib: Update to latest, which incorporates
a thread linking fix from Bruno Haible,
which was seen on newer Ubuntu systems.

diff --git a/gnulib b/gnulib
index 0b4e1419cd2fa7ce70c936f161db6d4c1825a798..16aa5a2efe82e01a147b4022258fa9a272f67625 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 0b4e1419cd2fa7ce70c936f161db6d4c1825a798
+Subproject commit 16aa5a2efe82e01a147b4022258fa9a272f67625