[llvm] Add unit tests for getUnderlyingObject (PR #89120)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

TBH I'd rather not have (IR) unit tests unless lit tests are uniquely hard to write for some reason. They are very annoying to update if they ever break. getUnderlyingObject() can be (and is) tested through its impact on alias analysis etc.

https://github.com/llvm/llvm-project/pull/89120