super glue / adhesive for plastic that is resilient to extreme temperature variation
I had something similar happen, and I was able to take out the screws from the inside of the car so the whole broken assembly could be taken inside.

Even though product recommendations are off topic, you should be able to find a good plastic adhesive at any hardware store.

You’d be best off with your adhesive results if you can add a bolt between the two pieces to keep them from moving or flexing the adhesive too much. If you remove the pieces from the car you can probably hide the fastener completely (it depends on how it broke). Clamp the two pieces together and give them plenty of time to cure (check the adhesive on the cure time) before putting it back on your car and into the elements.