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

[Freddy Ye via cfe-commits]

FreddyLeaf wrote:

Keeping `-march` supports for knl/knm meanwhile removing the specific ISA's intrinsic supports doesn't sound quite good to me. And thanks @phoebewang mentioned, removing the KNL/KNM supports could make all other targets always support AVX512F and AVX512VL meanwhile. This can simplify large amounts of logic codes in backend, which is very beneficial.

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