[compiler-rt] [compiler-rt][RISCV] Avoid using __init_riscv_feature_bits as a direc… (PR #115316)

[Kito Cheng via llvm-commits]

kito-cheng wrote:

> Given your recent update to the wording in C api, can you check that the lengths are being left as zero until e.g. hwprobes are successful? The setting of lengths on (new) line 359/360 looks a little strange to me, given (new) line 369 seems to return if initHwProbe fails.

Yeah I think that should fix as well, but let me create another PR for that :)

https://github.com/llvm/llvm-project/pull/115316