[llvm] PPC750cl, and initial support for paired singles (PR #211463)

[Cynthia Coan via llvm-commits]

Mythra wrote:

> I don't know if this has been mentioned yet. llvm will try to emit `lwsync` for the regular `750` and the 750cl doesn't support i think so hopefully this can be done in the pr

I think in general it’s best to keep this PR as small as possible in ease for review. When working in actual emitting code changes (like emitting Paired Singles), we can absolutely fold that in.

https://github.com/llvm/llvm-project/pull/211463