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

[William Junda Huang via llvm-commits]

huangjd wrote:

Added a test case. It is very contrived, and I think in real life only when using thinLTO + function pointer template parameter in source code has a potential to trigger it, and building clang itself is one example 

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