strdup() is not a C99 function (it's POSIX), not available in emscripten

On OpenGL ES it was set to use GL_CLAMP_TO_EDGE wrap mode for textures.
On LoadOBJ() texture coordinates were wrongly Y-flipped

[rlgl] Extensions strings loading was redone to avoid a Segmentation
Fault on Raspberry Pi

Splitted into:
UpdateCamera()             // Update only camera
UpdateCameraPlayer()   // Update camera and player position