[HardwareLoops] Optimisation remarks

This adds the initial plumbing to support optimisation remarks in
the IR hardware-loop pass.

I have left a todo in a comment where we can improve the reporting,
and will iterate on that now that we have this initial support in.

Differential Revision: https://reviews.llvm.org/D68579

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374980 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed