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

[Piyou Chen via llvm-commits]

BeMg wrote:

1. Let the caller to manage and construct the necessary key/value pairs for hwprobe, eliminating the need for the runtime site to sync with the hwprobe key table.
2. Modify __riscv_ifunc_select to accept a pointer to riscv_hwprobe and its length, so the prototype does not need to be updated when the hwprobe keys increase or change.

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