Well, I haven’t figured out how to use Zink yet, but I did finally discover a way to use OpenGL on macOS 11.6:
gcc \
-lgl \
-lglut \
-L /opt/X11/lib \
-I /opt/X11/include \
-o build/01-03_spinning_square \
opengl-programming-guide-seventh-edition/01-03_spinning_square.c && \
echo compiled && \
build/01-03_spinning_square
I don’t remember where /opt/X11 came from but I read something that said /opt/X11/ is created when Xquartz is installed.