build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 439b0e925f9ffb6fe58481717def708af96a9321..c96bab3fee48a9df55e7366344f838e1fc785c28 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 439b0e925f9ffb6fe58481717def708af96a9321
+Subproject commit c96bab3fee48a9df55e7366344f838e1fc785c28