Removed unused function warnings + others (Linux).
Removed unused function warnings + others (Linux).

* Moved functions only used by DX11/OpenGL under their own define
* Added 'fallthrough' comments to silence GCC's new fallthrough warnings
* Fixed endian code to actually be used as opposed to ignored (Fixes #101)

Celtoys/Remotery,Celtoys/Remotery,Celtoys/Remotery