[llvm] [LTO] Drop the weak function if there is a non-weak global symbol (PR #76287)

[Teresa Johnson via llvm-commits]

teresajohnson wrote:

> @teresajohnson This is `ModuleLinker` that mostly affects FullLTO, rather than thinLTO. I don't remember how `lld` implements fullLTO, is it not using `ModuleLinker` at all?

Forgot to respond to this question before. Right, lld and other new LTO API users do not use the ModuleLinker, but rather invoke the IRMover [directly](https://github.com/llvm/llvm-project/blob/6ad4ed5f1dd0a8160cd3c7b75e63a0e2f6061b5b/llvm/lib/LTO/LTO.cpp#L991).

https://github.com/llvm/llvm-project/pull/76287