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

[Freddy Ye via cfe-commits]

FreddyLeaf wrote:

And here're two more reasons I collected from gcc:
1. previously ICC and ICX has removed the support and emitted errors
1. we would also like to remove the support in GCC to reduce maintainence effort.

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