[WayneS]

Which provisions are those?

[Eagle Eye]

IMO Article 1 section 8 has everything needed to hire contract soldiers and sailors.

[JamesP81]

Which provisions are those?

Letters of marque, I believe is the term.

[An.American.Expatriate]

Which provisions are those?

Article 1, Section 8

...
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;

Letter of Marque
Archaic. A letter of marque was issued by a nation to a privateer or mercenary to act on the behalf of that nation for the purpose of retaliating against another nation for some wrong, such as a border incursion or seizure.

Reprisal
Archaic. An act taken by a nation, short of war, to gain redress for an action taken against that nation. For example, seizing a ship in retaliation for a seized ship.