Function gl::CompressedTexSubImage2D

pub unsafe fn CompressedTexSubImage2D(target: GLenum,
                                      level: GLint,
                                      xoffset: GLint,
                                      yoffset: GLint,
                                      width: GLsizei,
                                      height: GLsizei,
                                      format: GLenum,
                                      imageSize: GLsizei,
                                      data: *const c_void)

Fallbacks: CompressedTexSubImage2DARB