[llvm] [SeperateConstOffsetFromGEP] Handle `or disjoint` flags (PR #76997)

[Nikita Popov via llvm-commits]

nikic wrote:

> Looks like removing the NoBitsInCommon checks breaks an existing test - would it make more sense to go annotate said test with `disjoint` or to keep the check?

Annotate the test, assuming the flag would be present coming out of the middle-end (presumably yes).

https://github.com/llvm/llvm-project/pull/76997