[Polly][NewPM] Port CodeGen to the new PM
Summary: To move CG to the new PM I outlined the various helper that were previously members of the CG class into free static functions. The CG class itself I moved into a header, which is required because we need to include it in `RegisterPasses` eventually.
Reviewers: grosser, Meinersbur
Reviewed By: grosser
Subscribers: pollydev, llvm-commits, sanjoy
Tags: #polly
Differential Revision: https://reviews.llvm.org/D33423
git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@303624 91177308-0d34-0410-b5e6-96231b3b80d8