[LoopDist] Port to new PM

Summary:
The direct motivation for the port is to ensure that the OptRemarkEmitter
tests work with the new PM.

This remains a function pass because we not only create multiple loops
but could also version the original loop.

In the test I need to invoke opt
with -passes='require<aa>,loop-distribute'.  LoopDistribute does not
directly depend on AA however LAA does.  LAA uses getCachedResult so
I *think* we need manually pull in 'aa'.

Reviewers: davidxl, silvas

Subscribers: sanjoy, llvm-commits, mzolotukhin

Differential Revision: https://reviews.llvm.org/D22437

llvm-svn: 275811