[llvm] [VPlan] Retain exit conditions and edges in initial VPlan (NFC). (PR #137709)

[via llvm-commits]

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

This is fine w/ me, adding some last final comments, thanks!
@david-arm - is this ok w/ you?

https://github.com/llvm/llvm-project/pull/137709