[llvm] X86: Stop overriding getRegClass (PR #155128)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> @KanRobert with the changed tests, there are visible codegen changes. There are no machine verifier failures, as there should be if this were truly invalid. Can you take on using RegClassByHwMode for this? That would get you free verifier errors and then we can drop the virtual on getRegClass

You will get failures when compiling to binary, e.g., `-filetype=obj`

https://github.com/llvm/llvm-project/pull/155128