[clang] [X86] Emit Warnings for frontend options to enable knl/knm. (PR #75580)

[Shengchen Kan via cfe-commits]

KanRobert wrote:

One more justification...
https://www.felixcloutier.com/x86/vscatterpf0dps:vscatterpf0qps:vscatterpf0dpd:vscatterpf0qpd

The assembler support for some KNL instructions is buggy

https://github.com/llvm/llvm-project/blob/31429e7a89590f88034920edd3e997aeabff8124/llvm/test/MC/X86/apx/evex-format-intel.s#L46

If we deprecate KNL, the bug can go away.

https://github.com/llvm/llvm-project/pull/75580