[llvm] [Coroutines] fix coroutines + std::unique_ptr with async exceptions validation errors (PR #149691)

[Weibo He via llvm-commits]

NewSigma wrote:

> If you find it that critical, I can make the 6 tests have proper scope ends, it should not change the logics I try to mimic, that fails before the patch and passes afterwards.

Let's set it aside and see if @ChuanqiXu9 has further feedback. If it turns out to be a problem, we can fix it afterwards.

https://github.com/llvm/llvm-project/pull/149691