return auto_vec from get_dominated_by

return auto_vec from get_dominated_by

Signed-off-by: Trevor Saunders <tbsaunde@tbsaunde.org>
gcc/ChangeLog:

	* dominance.c (get_dominated_by): Return auto_vec<basic_block>.
	* dominance.h (get_dominated_by): Likewise.
	* auto-profile.c (afdo_find_equiv_class): Adjust.
	* cfgloopmanip.c (duplicate_loop_to_header_edge): Likewise.
	* loop-unroll.c (unroll_loop_runtime_iterations): Likewise.
	* tree-cfg.c (test_linear_chain): Likewise.
	(test_diamond): Likewise.