[clang] [llvm] [coroutine] Implement llvm.coro.await.suspend intrinsic (PR #79712)

[Chuanqi Xu via llvm-commits]

https://github.com/ChuanqiXu9 commented:

I got the reason why I felt `__await_suspend_helper_` was odd. In my imagination, we only need to emit the function `await_suspend(handle)` to an LLVM function and pass that to `llvm.coro.await.suspend` directly.

https://github.com/llvm/llvm-project/pull/79712