A character can only take at most one bonus action in their turn.
Bonus Actions, PHB p. 189:
You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.
Frenzy, PHB p. 19:
you can make a single melee weapon attack as a bonus action on each of your turns after this one.
Great Weapon Fighter, p. 167:
On your turn, when you ... reduce a creature to 0 hit points with [a melee weapon], you can make one melee weapon attack as a bonus action.