build: update gnulib submodule to latest

diff --git a/gnulib b/gnulib
index a65f999035e18eb802e5cf8b624ae15620ee67fa..d268b4b9646954b4a3b27fa924cf217b09e5acc1 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit a65f999035e18eb802e5cf8b624ae15620ee67fa
+Subproject commit d268b4b9646954b4a3b27fa924cf217b09e5acc1