dependencies, from OpenBSD. arc4_lock and sha512 in compat.
This makes arc4random available on all platforms, except when
compiled with LIBNSS (it uses libNSS crypto random).
git-svn-id: https://unbound.nlnetlabs.nl/svn/trunk@3158 be551aaa-1e26-0410-a405-d3ace91eadb9