[llvm] [VPlan] Fix WideIVStep wrap-flags (PR #191284)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. One nit is that the PR title could maybe be updated to something like "Preserve WideIVStep wrap-flags", because fix makes me think this is a correctness issue otherwise

https://github.com/llvm/llvm-project/pull/191284