Model statement wise reduction dependences

+ Collect reduction dependences
+ Introduced TYPE_RED in Dependences.h which can be used to obtain the
  reduction dependences
+ Used TYPE_RED to prevent parallelization while we do not have a privatizing
  code generation
+ Relax the dependences for non-parallel code generation
+ Add privatization dependences to ensure correctness
+ 12 Test cases to check for reduction and privatization dependences

llvm-svn: 211369