[llvm] [RISCV] Add support for getHostCPUFeatures using hwprobe (PR #94352)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Do you offer an alternative/default implementation when __NR_riscv_hwprobe is not available, e.g., in docker containers?

https://github.com/llvm/llvm-project/pull/94352