build: update from *public* gnulib

* gnulib: Update submodule to latest.
Kamil Dudka reported that bootstrap was broken.

diff --git a/gnulib b/gnulib
index 17017ae038b5b369d83b470c882fb4ceb388df1d..7d8f602d6f6c1ac2633c23140c93aaca098c6a2a 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 17017ae038b5b369d83b470c882fb4ceb388df1d
+Subproject commit 7d8f602d6f6c1ac2633c23140c93aaca098c6a2a