mkhash, I believe, is built from source by the build system. As such, I suspect that the "real" error occurs earlier in your build.
I didn't see ./scripts/feeds install -a in your process, though that should be "optional" and probably not the root cause.
A parallel build can cause problems with a fresh or significantly updated build tree. I didn't see if you were executing make -jN. Most of those parallel "start-up" issues can be mitigated with make -jN clean download world
The latest "official" list of dependencies for Debian I have is from
Some of that list, like buildbot-slave, probably aren't required for stand-alone builders. I don't think subversion is required, except perhaps for some "optional" packages that I don't use.
[GNU] time is no longer required, at least on master (I don't build 18.06, so can't confirm).