As
1) currently we can control brightness levels on illumos only on some
Toshiba laptops
2) this code knows nothing about illumos,
we disable blacklight helper to avoid warnings like:

** (mate-power-backlight-helper:82740): WARNING **: failed to find any devices:
 Error opening directory '/sys/class/backlight': No such file or directory

--- mate-power-manager-1.18.1/src/gpm-backlight-helper.c.1	2018-01-11 12:08:34.614360138 +0000
+++ mate-power-manager-1.18.1/src/gpm-backlight-helper.c	2018-01-11 12:38:20.646912292 +0000
@@ -160,6 +160,10 @@
 	gchar *filename_file = NULL;
 	gchar *contents = NULL;
 
+#if defined(__sun) && defined(__SVR4)
+	return GCM_BACKLIGHT_HELPER_EXIT_CODE_FAILED;
+#endif 
+
 	const GOptionEntry options[] = {
 		{ "set-brightness", '\0', 0, G_OPTION_ARG_INT, &set_brightness,
 		   /* command line argument */