Allow general loops with one latch

  As we do not rely on ScalarEvolution any more we do not need to get
  the backedge taken count. Additionally, our domain generation handles
  everything that is affine and has one latch and our ScopDetection will
  over-approximate everything else.

  This change will therefor allow loops with:
    - one latch
    - exiting conditions that are affine

  Additionally, it will not check for structured control flow anymore.
  Hence, loops and conditionals are not necessarily single entry single
  exit regions any more.

Differential Version: http://reviews.llvm.org/D12758

llvm-svn: 247289