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

[Sirui Mu via cfe-commits]

Lancern wrote:

PR #165556 removed the `__builtin_ia32_t2rpntlvwz*` builtins from clang and it landed a few hours ago, which causes ClangIR CI to fail. I just pushed a commit https://github.com/llvm/llvm-project/commit/7eef868892d05c363c9f42de67982c25afc348c6 directly to `main` to remove these builtins from our sources.

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