That was my first thought, but you can't really do that because `MacOS::X11.lib` raises an exception. To do that we'd need to fix `MacOS::X11.lib` to handle the case where neither `/opt/X11/lib/libpng.dylib` nor `/usr/X11/lib/libpng.dylib` exist.

```
Error: undefined method `/' for nil:NilClass
/usr/local/Library/Homebrew/os/mac/xquartz.rb:115:in `lib'
```