[Lsb-infrastructure] devchk glxext.h tests

[Denis Silakov]

I can see that devchk build using system compiler fails on glxext.h
tests. To correct this, 'GL_glxext_h.inc' file should be created inside
devchk folder with the following two lines:

#define GLX_GLXEXT_PROTOTYPES
#include <GL/glx.h>

Don't forget empty line at the end of file.

-- 
Regards,
Denis.