Fix MacOS SDL3 build

[jean-dao]

This IMG_ImageIO.m file is required to build on MacOS.

[jayschwa]

Thanks. I'll probably merge, but a couple questions first:

• Is the package currently broken on MacOS? Or do you just want to use the native framework?
• With this change, have you verified that it's actually using the correct code path? To use the native framework, I would have guessed that some new macro definition is required to replace / in addition to lib.root_module.addCMacro("USE_STBIMAGE", "");

[jean-dao]

* Is the package currently broken on MacOS? Or do you just want to use the native framework?

The package builds fine on its own, but IMG_Load is not included so it's not usable.

* With this change, have you verified that it's actually using the correct code path? To use the native framework, I would have guessed that some new macro definition is required to replace / in addition to `lib.root_module.addCMacro("USE_STBIMAGE", "");`

Actually, it is working because the native frameworks are linked by the SDL lib. Should it be explicitly linked here as well?

[jayschwa]

Actually, it is working because the native frameworks are linked by the SDL lib. Should it be explicitly linked here as well?

Yeah, any libraries or frameworks that ImageIO.m requires should probably be explicitly linked.

[jean-dao]

Frameworks used explicitly linked on both branches.