Annotate the IslAst with broken reductions

  + Split all reduction dependences and map them to the causing memory accesses.
  + Print the types & base addresses of broken reductions for each "reduction
    parallel" marked loop (OpenMP style).
  + 3 test cases to show how reductions are now represented in the isl ast.

  The mapping "(ast) loops -> broken reductions" is also needed to find the
  memory accesses we need to privatize in a loop.



git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@214489 91177308-0d34-0410-b5e6-96231b3b80d8