[llvm] [StructurizeCFG] nested-if zerocost hoist bugfix (PR #155408)

[Shilei Tian via llvm-commits]

shiltian wrote:

Ideally, I think it’d be better to revert your previous change, combine it with this one, run a CQE cycle, and if everything comes back green, reland it. But I'll leave that up to you.

https://github.com/llvm/llvm-project/pull/155408