[llvm] [LV][NFC] Query UnrollVectorizedLoop before executing the plan (PR #208500)

[David Sherwood via llvm-commits]

david-arm wrote:

If it is impossible to write a test for these changes, is it worth just folding this PR into https://github.com/llvm/llvm-project/pull/205102? Thoughts @fhahn?

https://github.com/llvm/llvm-project/pull/208500