Refactor exit PHI handling in vectorizer epilogue peeling
This refactors the handling of PHIs inbetween the main and the
epilogue loop. Instead of trying to handle the multiple exit
and original single exit case together the following separates
these cases resulting in much easier to understand code.
* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
Separate single and multi-exit case when creating PHIs between
the main and epilogue.