build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index acff3d22506764c18129317d2a8beb4af27ee28e..b6e096af3876e0e4093c0c885abe311a7cb9c3e5 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit acff3d22506764c18129317d2a8beb4af27ee28e
+Subproject commit b6e096af3876e0e4093c0c885abe311a7cb9c3e5