[llvm] [RemoveDIs] Add flag to preserve the debug info format of input IR (PR #87379)

[Orlando Cazalet-Hyams via llvm-commits]

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

Thanks, I think this is the only outstanding comment:

> Can you add comments (and update any flag description text if there is any) for the other flags explaining that they get overridden by this one?

LGTM with that done

https://github.com/llvm/llvm-project/pull/87379