[clang] [CIR] Emit CIR builtins: coroAlloc, coroBegin, and coroSize (PR #164180)

[via cfe-commits]

Andres-Salamanca wrote:

> Incremental progress towards upstreaming coroutine pieces in CIRGen, LGTM.
> 
> If you like this theme and are looking for more work around it, one possible followup is to work on LLVM lowering for cir.await, even though we don't have that in incubator yet.

Sure I’d be happy to work on that. I can finish upstreaming what’s already in the incubator first, and then start working on the LLVM lowering.

https://github.com/llvm/llvm-project/pull/164180