re PR tree-optimization/51269 (Vectorization profitability threshold is not actually used)

        PR tree-optimization/51269
        * tree-vect-loop-manip.c (set_prologue_iterations): Make
        first_niters a pointer.
        (slpeel_tree_peel_loop_to_edge): Likewise.
        (vect_do_peeling_for_loop_bound): Update call to
        slpeel_tree_peel_loop_to_edge.
        (vect_gen_niters_for_prolog_loop): Don't compute
        wide_prolog_niters here.  Remove it from the parameters list.
        (vect_do_peeling_for_alignment): Update calls and compute
        wide_prolog_niters.

From-SVN: r182844