I'd like to ask whether anyone who has a Mac with 10.11 or 10.12 might be willing to test out a portfile for me before I submit the PR.
The upstream devs bumped the minimum required versions of macOS and Xcode in Blender 2.90, but other than saying "require relatively recent versions" in the change log, they don't really give a good reason for doing this. I patched/reverted the version numbers using my portfile, and it still seems to compile fine on my machine. However, I no longer have any way of testing it, because my 10.11 machine has fallen victim to the 2011 MacBook Pro GPU flaw.
Here are instructions for how to test my new portfile:
Grab my portfile (and also everything inside the files/ folder), and do a "port install" on it.
See whether you can zoom in and out using the mouse scroll wheel. If you have a physical mouse scroll wheel that you can click, then try holding down the scroll wheel and dragging your mouse around inside the viewport to rotate the camera around the scene.
Try rendering a still image of the scene by hitting the F12 key. If you're feeling brave and believe that your machine is powerful enough, you can try rendering the entire animation by hitting Command-F12. (Note: Rendering animations is resource intensive and can take a very long time!)
If Blender fails to behave as expected or crashes at any point during my instructions, please let me know. Conversely, if everything worked without any problems, please also let me know.