Move vector highpart emulation to the optabs layer

Move vector highpart emulation to the optabs layer

        * expmed.c (expmed_mult_highpart): Rename from expand_mult_highpart.
        (expmed_mult_highpart_optab): Rename from expand_mult_highpart_optab.
        * optabs.c (can_mult_highpart_p): New.
        (expand_mult_highpart): New.
        * expr.c (expand_expr_real_2) [MULT_HIGHPART_EXPR): Use it.
        * tree-vect-generic.c (expand_vector_operations_1): Don't expand
        by pieces if can_mult_highpart_p.
        (expand_vector_divmod): Use can_mult_highpart_p and always
        generate MULT_HIGHPART_EXPR.
        * tree-vect-patterns.c (vect_recog_divmod_pattern): Likewise.
        * tree-vect-stmts.c (vectorizable_operation): Likewise.

From-SVN: r189407