swift234

[loops] Extract out loop simplification routines from LoopRotate.cpp into its own file, LoopUtils.{h,cpp}.

Currently we only expose canonicalizeLoop(). If we need more routines, we can
add/expose them.

The reason why this is separate from CFG.h is that all of the routines in CFG.h
that deal with loops just update loop information given a transformation, rather
than have a specific loop based transformation that they perform.

Swift SVN r31609