[llvm] [LoopUnroll] Add `prepare-for-lto` pass option (PR #192153)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

> How would you like to address this?

Hi @perry-ca, I can't reproduce this. Isn't `LoopFullUnrollPass::PrepareForLTO` used [here](https://github.com/llvm/llvm-project/blob/6ced989b95637a810f5cf160f22e28faa2f1754f/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp#L1663)?

https://github.com/llvm/llvm-project/pull/192153