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

[Matin Raayai via llvm-commits]

matinraayai wrote:

@nikic @arsenm I made another PR at #116290, but if the test CI won't be able to report any potential issues with the experimental targets I'm not sure how I can proceed besides building my fork on my local machine for all targets.

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