build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index 84ddfc7bd29853ed91cdd65c7ce818072959f974..6bb58afd0e0c21a5260a3a5b4a2dc94e8e2e2a6d 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 84ddfc7bd29853ed91cdd65c7ce818072959f974
+Subproject commit 6bb58afd0e0c21a5260a3a5b4a2dc94e8e2e2a6d