build: update gnulib submodule to latest

Note tests/init.sh and bootstrap are still in sync with gnulib.

* gnulib: Sync two configure check fixes.
- Avoid generating core dumps from regex configure check
- Fix compile error in getcwd configure check

diff --git a/gnulib b/gnulib
index 8209e72bf20d2b582384e91fde65df4f848a3a04..fba20d159fe191b9d67688738b7c31e769171aac 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 8209e72bf20d2b582384e91fde65df4f848a3a04
+Subproject commit fba20d159fe191b9d67688738b7c31e769171aac