[clang] [CIR][X86] Implement lowering for AVX512 mask builtins (PR #169774)

[via cfe-commits]

GeneraluseAI wrote:

@andykaylor @HendrikHuebner   Sorry for the earlier noise — the previous branch was based on an outdated fork.
This PR is rebased cleanly on main.

https://github.com/llvm/llvm-project/pull/169774