build: update gnulib for stringeq adjustment

* gnulib: Pull in stringeq adjustment.

diff --git a/gnulib b/gnulib
index 395bd7a734a1c0beb4daa25130c4a1cdfad5719d..b9f485800d15c795eca7d4512e1c3c88a64d2efd 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 395bd7a734a1c0beb4daa25130c4a1cdfad5719d
+Subproject commit b9f485800d15c795eca7d4512e1c3c88a64d2efd