[llvm] [MachO] Preserve weak linkage for aliases (PR #198148)

[Folkert de Vries via llvm-commits]

https://github.com/folkertdev commented:

What's been done in terms of testing here? I know `rustc` needs this for the EEI (externally implementable items) feature, did someone test this end-to-end?

https://github.com/llvm/llvm-project/pull/198148