OpenBSD imports xz-utils

Ha ha ha...

I wouldn't be surprised, though, if xz were forked and imported, then reworked by the OpenBSD folks. Forgetting for a moment that it's April first, I thought that's what this would be ;)

> This commit imports the v5.6.1 release of xz-utils, replete with binary inputs in tests/files/ for regress testing.

Cute.

I'm half surprised that they didn't say something like "with only 2 vulns in base in living memory, we've resorted to importing them":P

Okay this got me.