[LoopDist/LoopVer] Move LoopVersioning to a new module, NFC

Summary:
The class will obviously need improvement down the road.  For one, there
is no reason that addPHINodes would have to be exposed like that.  I
will make this and other improvements in follow-up patches.

The main goal is to be able to share this functionality.  The
LoopLoadElimination pass I am working on needs it too.  Later we can
move other clients as well (LV and Ashutosh's LICMVer).

Reviewers: hfinkel, ashutosh.nema

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10577

llvm-svn: 241932