[llvm] [llvm-opt-report] Show scalable vectorization factors (PR #123367)

[via llvm-commits]

iamlouk wrote:

@nikic , as I can't find another still-active contributor and there is no maintainer assigned to this, would you mind taking a look at the PR (and in case you approve, click the merge button for me?). Thank you very much in advance, sorry for the disturbance.

https://github.com/llvm/llvm-project/pull/123367