complete LLVM toolset in 10.0?

LLVM is now partially installed in the base system, but for some
development and research purposes I need other parts of LLVM like
llc, lli, llvm-as and buddies. I miss them.

Is there a chance to get them reeled into the build tree via a knob in
/etc/src.conf? I'd like to see them available in 10.0.

I also file a PR not to loose track on that.

Oliver