I believe it is in fact an upgraded version of the CS Odjur, so that could mean that Capstone, in a way, built it, but if the Medician Government is the one that introduced the upgrades, wouldn't they technically be the manufacturer? And I also heard in mission dialogue in the mission Three's Company that the Black Hand may have helped develop it if not developed it themselves. Additionally Tom Sheldon in that same mission states that the tanks have come from "Your friendly neighborhood Agency of course!"
Overall there are four theorized manufacturers of this tank, so who built it?