build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index a359f602d3e5a29f9381e70cc7e14a24a65e54ab..30fcbcc4db4973f84999a00c30e490e39989e96e 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit a359f602d3e5a29f9381e70cc7e14a24a65e54ab
+Subproject commit 30fcbcc4db4973f84999a00c30e490e39989e96e