[compiler-rt] [compiler-rt][RISCV] Implement __init_riscv_feature_bits (PR #85790)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

And to be clear, I'm not saying that anything should be blocked on getting FreeBSD supported. I'm just saying that one of the benefits of this interface is that it can be reused on other OSes in future PRs, all that's needed is implementing it for that OS in compiler-rt, which is completely doable for any OS.

https://github.com/llvm/llvm-project/pull/85790