For those who wish to run Yolov3 on your macbook, here is a note you might to checkout for your installation.
First, git clone https://github.com/AlexeyAB/darknet. Make sure you are not using the outdated darknet.
Second, download the attachment from this gist, namely Makefile and opencv.pc, and place them in the cloned repository, which overwrites the original Makefile, for sure.
Third, depending on your opencv installation location, you might want to change prefix in opencv.pc. In the example, I am giving here, I have installed opencv with conda and therefore the library sits in one of my virtual environments. If you wish not to use opencv, change OPENCV=0 in Makefile.
Four, if you wish to use openmp, then brew install libomp. Otherwise, change OPENMP=0 in Makefile.