[clang] [CIR] Add missing coroutine plumbing (PR #222472)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> > @Andres-Salamanca has been working on the coroutine support for quite a while (blocked mostly by my slowness in review), and I'm concerned that parts of this will diverge from what he has planned following #213191).
> 
> Thank you for letting me know! I'll close this chain then.
> 
> On a side note, is there a CIR CORO TODO list? I'm using CIR for unrelated reasons, but coroutine support is crucial for my case, so I'd be willing to help as much as I can.

As Andres noted, we don't have a TODO list apart from the markers in the code. In addition to the pieces Andres suggested, it would be a huge help if you could review Andres' patches. Having another person who is familiar with the intricacies of coroutines providing input would be extremely valuable.

https://github.com/llvm/llvm-project/pull/222472