[llvm] [InstCombine] Push freeze through non-recurrence PHIs (PR #157678)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

I've rebased and added a fix for the compile-time issue in spec2017 527.cam4_r, although I'm unable to write a test for it. This IR hits the fix I've added: https://godbolt.org/z/KrTcWroqr, initially I bailed out here but it caused a regression, so I changed it to not freeze the poison value instead.

https://github.com/llvm/llvm-project/pull/157678