[llvm] [VPlan] Update final exit value via VPlan. (PR #112147)

[David Sherwood via llvm-commits]

david-arm wrote:

Hi @fhahn, whilst attempting to rebase https://github.com/llvm/llvm-project/pull/120567 on top of this PR I noticed failures when building the LLVM test suite. Apologies in advance if you're already aware! Just for reference, the error I see is:

```
clang: /home/davshe01/regression/llvm/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp:3138: virtual void llvm::VPWidenPointerInductionRecipe::execute(llvm::VPTransformState&): Assertion `
!onlyScalarsGenerated(State.VF.isScalable()) && "Recipe should have been replaced"' failed.
```

https://github.com/llvm/llvm-project/pull/112147