Fix reading pixels on little-endian systems

[Gorggg]

This fixes an issue where glReadPixels read components out-of-order on little-endian machines, leading to resulting images with inaccurate color values. To fix this, we make the pixel format value conditional on cpu endianness, which we get CMake to identify at compile time.

Thank you for reading this. If there is anything I can improve, please let me know.

[landswellsong]

Hello. Sorry I completely forgot about this repo. I'll get back to you as soon as I have time to brief myself back about what was going on here.

[Gorggg]

Thanks for the reply. My experience of this issue was that images resulting from glReadPixels() had distorted colors. I determined that this was because the resulting format was endianness-dependent, therefore they were reversed in certain scenarios. I fixed the issue by detecting endianness at compile-time and adjusting the format of the operation accordingly.

If there is anything more I can help you recall or clarify, please let me know, and thank you for your time.