[clang] [CIR][NFC] Add infrastructure for handling X86 builtins (PR #164465)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

@woruyu This PR added the infrastructure needed for https://github.com/llvm/llvm-project/issues/163895. You'll need to break up the giant switch statement of currently unimplemented x86-builtins, but please leave them in the current order. Just duplicate the NYI error call for the block above the builtins for which you are adding the implementation.

https://github.com/llvm/llvm-project/pull/164465