[clang] [compiler-rt] [llvm] [X86] Add missing checks for attribute target testing and support AVX5124VNNIW/4FMAPS in compiler-rt (PR #218697)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

IIRC we only support AVX5124VNNIW/4FMAPS as assembly now, we've tended to assume that if anyone is targeting knights landing workloads they will downcode.

I think eventually we'll end up with something similar for MMX as well, but there's a lot more "support" still lingering inside llvm at the moment.

https://github.com/llvm/llvm-project/pull/218697