[llvm] [VPlan] Model branch cond to enter scalar epilogue in VPlan. (PR #92651)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Addressed comments, a number of tests need updating after the recent changes (using a regular VPBB for the scalar.ph initially, don't reorder incoming blocks)

https://github.com/llvm/llvm-project/pull/92651