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

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

@paulwalker-arm thanks for taking a look, I think your analysis makes sense. I have previously looked at 1. as @nikic also suggested, but found it a bit tricky. I've had a go at 2., it's quite a simple change and does address the issue.

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