[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:

This patch is to fix a bug encountered while bootstrapping clang itself, I was not able to create a minimum reproducing case. The failing case happens in a thinLTO step involving a lot of files so it is unrealistic to make it a test case. 

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