build: update gnulib submodule to latest

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

* gnulib: Sync many fixes/changes, including the base64
encoding speedup mentioned in commit v8.21-145-g9120845
Also included is support for enabling use of libcrypto hash routines
which are generally well optimized for particular systems.

diff --git a/gnulib b/gnulib
index 798e9bc8b86c1032105682771539bae4ea1e9128..8209e72bf20d2b582384e91fde65df4f848a3a04 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 798e9bc8b86c1032105682771539bae4ea1e9128
+Subproject commit 8209e72bf20d2b582384e91fde65df4f848a3a04