[llvm] [Coroutines] Split buildCoroutineFrame into normalization and frame building (PR #108076)

[Yuxuan Chen via llvm-commits]

https://github.com/yuxuanchen1997 approved this pull request.

Overall I think a neutral/positive change. One thing I am worried was that how we are going to distinguish a "normalized" vs a "unnormalized" coroutine? i.e. How do we find out that we missed a normalization here? 

https://github.com/llvm/llvm-project/pull/108076