[llvm] [VPlan] Extract reverse mask from reverse accesses (PR #155579)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> LGTM w/ florian's comment. Also it looks like the Windows CI tests are failing but I'm not sure why. I've restarted the CI job hoping it's just a dodgy cache, but if it fails again we might need to look into it

cf381423eef2ced33c843f01aee483a008e556c6
Fixed the unspecified evaluation order. Hopefully, this resolves the Windows CI failures.

https://github.com/llvm/llvm-project/pull/155579