Working Rust m68k port demonstrated for MegaDrive

This is based on the M68k backend for LLVM which is currently being upstreamed:

> https://github.com/M680x0/M680x0-mono-repo

and the m68k Rust backend I am working on:

> https://github.com/glaubitz/rust/commits/m68k-linux

Anyone interested in supporting LLVM for M68k can contribute to the Bountysource campaign:

> https://www.bountysource.com/issues/90829856-llvm-complete-t...