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

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fpasserby wrote:

> Thanks. This looks good to me except few nit comments.
> 
> Have you tested on a real world workloads?

I've tested it on seastar and libcppcoro tests and on the example from #72006.

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