[clang] [llvm] [RISCV] Support __builtin_cpu_init and __builtin_cpu_supports (PR #99700)

[Piyou Chen via llvm-commits]

https://github.com/BeMg approved this pull request.

LGTM. Work fine with current compiler-rt `__init_riscv_feature_bits `/`__riscv_feature_bits ` and qemu with hwprobe support. 

https://github.com/llvm/llvm-project/pull/99700