[clang] [llvm] [coro] Lower `llvm.coro.await.suspend.handle` to resume with tail call (PR #89751)

[via llvm-commits]

zmodem wrote:

> The higher level idea looks fine.

Thanks!

> A detail is that, in this patch, we must not mark `llvm.coro.await.suspend.handle` as nounwind. Previously, `llvm.coro.await.suspend.handle` may be marked as nounwind if the `await_suspend` is noexcept. But we can't do it in this patch since `llvm.coro.await.suspend.handle` will include `resume` calls, which technically is not nounwind.

Done.

https://github.com/llvm/llvm-project/pull/89751