add option for newer Linux demos to dynamically load X11, glX and OpenGL 1 functions
(and avoid having to link against X, glx and GL)
-DGLEW_INIT_OPENGL11_FUNCTIONS
-DGLEW_DYNAMIC_LOAD_ALL_GLX_FUNCTIONS
-DDYNAMIC_LOAD_X11_FUNCTIONS
and link against libdl (for example usingi -ldl)