Updates to newer toolchains

[Serentty]

Along with rebasing the patches on a newer version of Rust occasionally, now that 68000 support has been upstreamed in LLVM, would it be possible to switch to mainline LLVM?

[ricky26]

Somehow I missed this comment, I'm very sorry.

At the moment, there's quite a few patches left in my LLVM branch which haven't made it into LLVM mainline (most notably, the mainline doesn't produce correct code for the 68000 variant wrt the CCR).