Add test case for LoopSink pass

This test checks that load from constant memory will be sunk regardless of
aliasing stores in the loop.

Patch by Daniil Suchkov!

Differential Revision: https://reviews.llvm.org/D39113


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316207 91177308-0d34-0410-b5e6-96231b3b80d8