map bb with pbb via hash

map bb with pbb via hash
Mark unused varialbe as ATTRIBUTE_UNUSED
Mark loops as parallel via dependency checking.

* graphite-clast-to-gimple.c (translate_clast): Mark newly created
  basic block and loop.
  (mark_bb_with_pbb): New.
  (unmark_bb_with_pbb): New.
  (dependency_in_loop_p): New.
  (mark_loops_parallel): New.
* graphite-dependences.c (check_dependency_between_pbbs): New.
* graphite-poly.c (new_poly_bb): Change return value from void to poly_bb_p.
* graphite-poly.h (new_poly_bb): Change declaration.
  (dependency_between_pbbs_p): Declare.
* graphite-sese-to-poly.c (new_gimple_bb): Remove bb->aux construction.
  (free_gimple_bb): Remove bb->aux destruction.
  (try_generate_gimple_bb): Mark bb with it's relevant poly_bb_p.
  (gbb_from_bb): Change parameter from basic_block to poly_bb_p.
* graphite.c (graphite_transform_loops): Mark loops parallel
via dependency checking.