[llvm] [ThinLTO] Do not duplicate import a function that is actually defined in the current module (PR #110064)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson commented:

Note that this code is also used by regular LTO, so this would not just affect ThinLTO.

I really hope that we can find a way to reproduce the failure with some kind of test.

https://github.com/llvm/llvm-project/pull/110064