make sdl_gpu divergent from upstream

[vddCore]

several issues exist in sdl_gpu that can only be resolved by gutting sdl_gpu and tweaking some stuff on our own, namely:

• error queue seems to be fucked up sometimes
• openGL renderer initialization sequence is less-than-stellar

additionally, doing this might pave the way for vulkan renderer down the line as i'll understand sdl_gpu architecture a little bit better