[llvm] [VPlan] Add VPIRInstruction, use for exit block live-outs. (PR #100735)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Updated and address comments now that https://github.com/llvm/llvm-project/pull/100658 has landed

https://github.com/llvm/llvm-project/pull/100735