Let's say I cast Golgari Charm (an instant) before my opponent attacks. I choose the "all creatures get -1/-1 until end of turn" and then my opponent attacks with, among other creatures, a Precinct Captain which says "whenever Precinct Captain deals combat damage to a player, put a 1/1 white Soldier creature token onto the battlefield".
If the Precinct Captain successfully deals combat do the 1/1 Soldier tokens it creates die instantly because of the Golgari Charm's "-1/-1 until end of turn" or do they survive because they weren't in play at the time the "-1/-1 until end of turn" took effect?