[llvm] [LTO] Add an option to select a pre-link pipeline (PR #82585)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

> Couldn't this also be achieved by using something like `-opt-pipeline='thinlto-pre-link<O3>'`?

yes, although I'm not a huge fan of asking people to use the stringly typed interface (even though that's what the C API is to construct passes...)

https://github.com/llvm/llvm-project/pull/82585