build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 6ef3d783333346333f35bb181ba90f5bc46c0b29..ff208d546a26fee39a0191297c11560da74b5dee 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 6ef3d783333346333f35bb181ba90f5bc46c0b29
+Subproject commit ff208d546a26fee39a0191297c11560da74b5dee