[llvm] Fixed un-renamed CodeGenTargetMachineImpl Intheritances in Experimental Targets (PR #116290)

[Matin Raayai via llvm-commits]

matinraayai wrote:

@arsenm I replaced some leftover mentions of `LLVMTargetMachine` in the comments. I built the experimental targets on my end and it seems to build fine, and the tests pass on my end. Let me know if there's anything else I need to fix on my part.
Sorry for breaking change.

https://github.com/llvm/llvm-project/pull/116290