[DeLICM] Use Known information when comparing Existing.Occupied and Proposed.Occupied.

Do not conflict if the value of Existing and Proposed are the same.

This change only affects unit tests, but no functional changes are
expected on LLVM-IR, as no Known information is yet extracted and
consequently this functionality is only triggered through unit tests.

Differential Revision: https://reviews.llvm.org/D32025

llvm-svn: 301301