"In the same way, we, believing in God, are made righteous, for 'through faith shall the righteous live'; so 'the promise made to Abraham came not through the Law but through faith.' Since Abraham was made righteous by faith, and 'the Law is not laid for the righteous,' likewise, we are not made righteous by the Law, but by faith, which receives testimony from the Law and Prophets, and which the Word of God offers us" (1.35).
With the majority position, Irenaeus clearly sees "the righteous" in Romans 1:17 as the guilty sinner justified by faith. He takes Abraham to be the first to whom this justification was reckoned and all who believe in the God revealed in Jesus to be likewise justified. I do not always agree exegetically with the ancients, and I do sometimes go back and forth considering both sides in this particular case. I must say, though, that I often find the views of those who understood Paul's Greek much better than I to be quite persuasive. It is also comforting to find oneself in agreement with what has been taught in the church for nearly two millenia. That said, I presently find myself leaning towards Irenaeus' understanding of "the righteous."