build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 762bd0aa660b0c1c02597e0d2e5c5fbf9bab1b91..ff7a4ffc9e87339baa6e02ad10563137cd381474 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 762bd0aa660b0c1c02597e0d2e5c5fbf9bab1b91
+Subproject commit ff7a4ffc9e87339baa6e02ad10563137cd381474