[llvm] All function merger to be run during LTO link with gold plugin (PR #121343)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson approved this pull request.

This change looks ok to me. However, should this pass be enabled by default instead, maybe at least when optimizing for size? It's unfortunate to have to wire through options for individual passes like this. cc @aeubanks for thoughts since he has done some pass pipeline work.

https://github.com/llvm/llvm-project/pull/121343