CMake: Make the code more platform-agnostic and cleaner.
Support render-to-self on GLES2.
Don't use shader blending without buffers.

Ugh, making ComputeFragmentShaderID() slower again...
Support block transfer uploads in non-buffered.
Allow a memcpy upload in non-buffered rendering.
Merge pull request #6191 from unknownbrackets/gpu-minor

Allow uploads to framebuffers in non-buffered, disable shader blending
Switch to libpng17 to resolve NEON issue on iOS + other bug fixes.
Native update
Native buildfix
Qt: Update to libpng17. Update native.
Win32 buildfix.
Merge pull request #6194 from thedax/win32-buildfix

Win32 buildfix.
multiple SDL joystick support, initial commit untested