check_c_source_compiles("
#define GL_GLEXT_PROTOTYPES
#ifdef _USE_OPENGL_FRAMEWORK
# include <OpenGL/gl.h>
# include <OpenGL/glext.h>
#else
# include <GL/gl.h>
# include <GL/glext.h>
#endif

static void
DebugMessageCallback(GLenum source, GLenum type, GLuint id, GLenum severity,
    GLsizei length, const GLchar *message, const void *userParam)
{ }

int main(int argc, char *argv[]) {
	glEnable(GL_DEBUG_OUTPUT);
	glDebugMessageCallback(DebugMessageCallback, 0);
	return (0);
}
" HAVE_GLEXT)