[llvm] [VPlan] Add exit phi operands during initial construction (NFC). (PR #136455)

[via llvm-commits]

================
@@ -9388,11 +9387,8 @@ collectUsersInExitBlocks(Loop *OrigLoop, VPRecipeBuilder &Builder,
         continue;
----------------
ayalz wrote:

Independent: loop-unswitch this condition
```
      if (ExitVPBB->getSinglePredecessor() != Plan.getMiddleBlock()) {
        assert(ExitIRI->getNumOperands() ==
                   ExitVPBB->getPredecessors().size() &&
               "early-exit must update exit values on construction");
        continue;
```
rather than check it for all phi's?
assert can be removed given that the number of operands of all phi recipes should be equal to the number of predecessors - check in verifier instead?

https://github.com/llvm/llvm-project/pull/136455