[clang] [llvm] [RISCV] Add riscv_atomic.h and Zawrs/Zalrsc builtins (PR #94578)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

If we are talking about the necessariness of adding these intrinsics, please refer to the ARM implementations in DPDK (https://github.com/DPDK/dpdk/blob/76cef1af8bdaeaf67a5c4ca5df3f221df994dc46/lib/eal/arm/include/rte_pause_64.h).We want to use 

https://github.com/llvm/llvm-project/pull/94578