build: update from gnulib, for latest maint.mk

* gnulib: Update submodule to latest.
This fixes the make syntax-check failure whereby sc_po_check
would complain about cfg.mk.

diff --git a/.gnulib b/.gnulib
index 1203e8d1f62dec3d2436dffadd5c20793cf84366..b653eda3ac4864de205419d9f41eec267cb89eeb 160000 (submodule)
--- a/.gnulib
+++ b/.gnulib
@@ -1 +1 @@
-Subproject commit 1203e8d1f62dec3d2436dffadd5c20793cf84366
+Subproject commit b653eda3ac4864de205419d9f41eec267cb89eeb