build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index b6e096af3876e0e4093c0c885abe311a7cb9c3e5..fb7312fa8d3df29f0ca0678f669b9a5b88a078ec 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit b6e096af3876e0e4093c0c885abe311a7cb9c3e5
+Subproject commit fb7312fa8d3df29f0ca0678f669b9a5b88a078ec