[llvm] CodeGenPrepare: Null check pointers (PR #142350)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

This cannot be fixed with an assert. It should be a tested fatal error, and I was hoping we could do this for every pass that requires the TargetMachine 

https://github.com/llvm/llvm-project/pull/142350