[llvm] [ADT] Make null PointerUnion with different active members compare equal (PR #121847)

[Jakub Kuderski via llvm-commits]

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

This seems unusual / unexpected to me, Do we have an example of similar semantics in some other LLVM type or an external library?

> Hm, I'm not really convinced this change is right. If PointerUnion allows having null pointers of different types, then treating them as equal may not be correct in general.
+1

https://github.com/llvm/llvm-project/pull/121847