build: update from gnulib, for rename.m4 fix, improved tests, etc.

* gnulib: Update submodule to latest.

diff --git a/gnulib b/gnulib
index c90c5cc82c3b0c07b2dff0f135be74bbb97e0b60..7fcb389fb4cd5ba26e330fef991ffdc05392f289 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit c90c5cc82c3b0c07b2dff0f135be74bbb97e0b60
+Subproject commit 7fcb389fb4cd5ba26e330fef991ffdc05392f289