IPA-CP: Always access param_ipa_max_agg_items through opt_for_fn

2020-01-10  Martin Jambor  <mjambor@suse.cz>

	* params.opt (param_ipa_max_agg_items): Mark as Optimization
	* ipa-cp.c (merge_agg_lats_step): New parameter max_agg_items, use
	instead of param_ipa_max_agg_items.
	(merge_aggregate_lattices): Extract param_ipa_max_agg_items from
	optimization info for the callee.

From-SVN: r280098