[llvm] [X86][EVEX512] Restrict attaching EVEX512 for default CPU only, NFCI (PR #65920)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

@ronlieb Thanks for reporting this issue! This exposed a bug not for this patch but a related one https://github.com/llvm/llvm-project/commit/24194090e17b599522a080d502ab0f68125d53dd, which should be solved by #70420.
Did you get the IR from a non Clang front end? With that change, FEs need to push a `+evex512` feature when they enable AVX512 features on a non AVX512 target (zen3 in this example) to keep the backward compatibility. Otherwise, there will be crash in the backend.

https://github.com/llvm/llvm-project/pull/65920