Implement _onSpinWait() intrinsic for RISC-V, and it can be implemented by using PAUSE instruction from Zihintpause Extension, which is ratified and a mandatory extension of RVA22U64 (https://github.com/riscv/riscv-profiles/blob/main/profiles.adoc#rva22u64-mandatory-extensions).
Software can use the PAUSE instruction to reduce energy consumption while executing spinwait
code sequences (https://github.com/riscv/riscv-isa-manual/blob/master/src/zihintpause.tex).