Commit a new LoopStrengthReduce pass that can use scalar evolutions and

Commit a new LoopStrengthReduce pass that can use scalar evolutions and
target data to decide which loop induction variables to strength reduce
and how to do so.  This work is mostly by Chris Lattner, with tweaks by
me to get it working on some of MultiSource.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22558 91177308-0d34-0410-b5e6-96231b3b80d8