build: update gnulib submodule to latest

* gnulib: Update including various build fixes.

diff --git a/gnulib b/gnulib
index 2a3dbe99a2aeb058ecb033d7d830e6600e16c91c..c610b4a9b289cb99dc78178a233b811614af9c26 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 2a3dbe99a2aeb058ecb033d7d830e6600e16c91c
+Subproject commit c610b4a9b289cb99dc78178a233b811614af9c26