build: update gnulib submodule to latest, for getfilecon wrappers

diff --git a/gnulib b/gnulib
index 6f6420cc9705dcfa545a28c674fddf5703e72c86..f4dc80620e25623a69aa852bec5a52e150cedd4a 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 6f6420cc9705dcfa545a28c674fddf5703e72c86
+Subproject commit f4dc80620e25623a69aa852bec5a52e150cedd4a