[llvm] [IPSCCP] Track returns of non-interposable definitions (PR #210374)

[Krzysztof Drewniak via llvm-commits]

https://github.com/krzysz00 approved this pull request.

I think this makes sense, but this is a weak approval since I'm trusting your descriptions of the semantics here

https://github.com/llvm/llvm-project/pull/210374