When building TIC-80 on architectures that don't have Ruby installed, the build fails. It would be great if we were still able to build TIC-80, just without the mruby support. While I understand it's possible to cross-compile it, it can be difficult to handle the target across all the platforms we're hitting.

Implementation

• Adds an option named BUILD_WITH_MRUBY, which defaults to TRUE when rake is found
• Uses BUILD_WITH_MRUBY to determine whether or not to enable mruby