Compilation errors without JO_COMPILE_USING_SGL

[iequalshane]

It looks like the engine doesn't currently compile if SGL is disabled. I had quite a few errors and a lot of VDP2 code calls sl* functions without an ifdef and alternative definition. Also, removing JO_COMPILE_USING_SGL from a project still ends up defining it because the code will set it to 1 if it doesn't exist.

[johannes-fetz]

I fix the compilation, but this option is broken unfortunately.
I don't know when I could finish the implementation without SGL.
However, the primary goal of the Jo-Engine is to make the platform accessible for developers and not to recode Sega libraries.