[clang] [llvm] [AArch64] Disable FEAT_RNG on Grace. (PR #166387)

[Ricardo Jesus via cfe-commits]

rj-jesus wrote:

> The part that alters -mcpu=grace sounds good. I believe that can be committed separately and isn't dependant on the rest. The part that alters Host.cpp is related to -mcpu=native and could be better included of the other patch, so that -mcpu=native works correctly.

Thanks, that should be done now. Depending on the PR that's merged first, I'll update the other to remove the corresponding FIXME.

> (I think how it would best work is to use hpcaps on linux and trust all the feaures we have, but that is a larger change).

Agreed, I think that's how we should be doing it. Maybe some of the FMV code in compiler-rt could be used for it?

https://github.com/llvm/llvm-project/pull/166387