[llvm] Overhaul the TargetMachine and LLVMTargetMachine Classes (PR #111234)

[Matt Arsenault via llvm-commits]

arsenm wrote:

Probably should do an RFC. If this has any impact it's probably on out of tree targets and users. I don't expect much feedback though, can post and give it a week or two 

https://github.com/llvm/llvm-project/pull/111234