[llvm] [UTC] Add initial VPlan support. (PR #178534)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> If we can wait for `print-after*` PRs to land, then this is how I've done the same on top of `print-after`: https://github.com/llvm/llvm-project/pull/178736/changes/5f5ccb54dbcb93932d8e3149bd8d0db688e76847..3ee1c5eff4da3d9c160c0f252de69d0f9906762e

Yep once that lands we can update UTC to support it and eventually drop the support via plain LoopVectorize debug output.

I don't have a strong opinion, just thought it may be good to add the initial support independently 

https://github.com/llvm/llvm-project/pull/178534