Strongmen via gameplan and teamwork.
This, and there are several strategies that might work. Assuming a total commitment- these guys know they are doomed- they know that and the gorilla does not understand. All he can do is rage out impressively for a few minutes and then fold. If they come at him like an 80's karate movie, sure the gorilla bitchslaps every one of them.
If the people skirmish with him by rushing him from behind in groups of 3 and scatter when he charges (gorillas are probably a touch more than 1.5 times as fast as a big guy at top speed), the gorilla is going to get tired very quickly and a couple people will probably get hurt. The gorilla will break psychologically after some time and give up like a lion to a pack of hyenas.
If they all rush him at once it's going to be ugly, but 12 strong men can overpower it limb by limb, and again, tire it out with the loss of maybe one or two of them. If one gets got, they can always regroup.
Hell, they can sit around doing nothing and wait for the fucker to fall asleep if they want to. Treat it like a dog, find its reactive distance and spend a few hours closing that distance and making the gorilla as comfortable as possible.
I'm confident in 12 winning, but I wonder what the number is that just stands no fucking chance in unarmed combat. Probably 5?