What is the usage of 子 in 「修我戈矛，与子同仇」? This particular phrase comes from《诗经·秦风·无衣》

Full: 岂曰无衣？与子同袍。王于兴师，修我戈矛。与子同仇！
Translation: 

Who said that you have no clothes to wear,

I will share with you my robe. 

The king has called upon us that,

we make ready with spears and Ge's (戈)，

we fight against our enemies.