St. Thomas Aquinas gives this precise objection in his question on "Whether it is lawful to kill oneself?" (Summa Theologica II-II q. 64 a. 5 arg 4):
Samson killed himself, as related in Judges 16:30, and yet he is numbered among the saints (Heb. 11:32). Therefore it is lawful for a man to kill himself.
To which he replies (ibid. ad 4):
As Augustine ...