[RFC] Backend for Motorola 6800 series CPU (M68k)

I looked at CodeBeadsGen.cpp. It looks good, as do the changes to TableGen.cpp and TableGenBackends.h. You might want to check out the new TableGen Backend guide to be sure you're following all the conventions. And obviously a good comment at the top explaining what a "code bead" is would be helpful.

https://llvm.org/docs/TableGen/BackGuide.html