DragonFly now has GCC 5.1 release. If you are running DragonFly master (i.e. 4.1), you’ll probably want to both rebuild world and kernel, and update your packages so they all match. There’s already packages built with GCC 5.1, so binary package upgrades can happen quickly. There’s GCC 4.7 packages still available if you aren’t making the jump yet.
If you’re on DragonFly 4.0.x – nothing’s changed.