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.

llvm-svn: 214489