[Test] Add a unit test exposing lack of SCEV invalidation in LICM during code hoisting. NFC.

This unit test exposes a bug in LICM: when it hoists instructions it doesn't invalidate SCEV accordingly.
Similar test exposing lack of SCEV invalidation during code sinking will be submitted as a follow-up change.

Patch Author: Daniil Suchkov
Reviewers: mkazantsev, asbirlea, reames
Reviewed By: asbirlea
Subscribers: mgorny, javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D69369