[clang] [llvm] [Coroutines] Use destroy slot for CoroElide resume fallthrough (PR #207799)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> > I feel it is overly complicated. Why can't we just replace the CoroEnd with the destroy ptr in resume function generally?
> 
> That would work too. However, it would be a pessimization for coroutines that are not marked await-elidable. The same code path became virtual when it didn't need to be.

Seems fine to me.

But we need to figure out why @StephanDollberg 's reproducer is still crashing. I feel it might be another issue.

https://github.com/llvm/llvm-project/pull/207799