[LoopInterchange] Add remark for calls preventing interchanging.

It also updates test/Transforms/LoopInterchange/call-instructions.ll
to use accesses where we can prove dependence after D35430.


Reviewers: sebpop, karthikthecool, blitz.opensource

Reviewed By: sebpop

Differential Revision: https://reviews.llvm.org/D45206

llvm-svn: 329111