[llvm] [CoroEarly] Hide promise alloca for later passes (PR #139243)

[Weibo He via llvm-commits]

NewSigma wrote:

Apologies for the incorrect function name earlier and I corrected it. To clarify, we lower coro.promise before the CoroFrame pass. These logics are essential for frame generation.

https://github.com/llvm/llvm-project/pull/139243