compositor: Setup weston-launch sock in fbdev

weston_launcher_open() was failing with:
    recvmsg: Socket operation on non-socket

Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>

src/compositor-fbdev.c

@@ -835,6 +835,15 @@ fbdev_compositor_create(struct wl_display *display, int *argc, char *argv[],
 	                           config) < 0)
 		goto out_free;
 
+	/* Check if we run fbdev-backend using weston-launch */
+	compositor->base.launcher_sock =
+		weston_environment_get_fd("WESTON_LAUNCHER_SOCK");
+	if (compositor->base.launcher_sock == -1 && geteuid() != 0) {
+		weston_log("fatal: fbdev backend should be run "
+			   "using weston-launch binary or as root\n");
+		goto out_compositor;
+	}
+
 	compositor->udev = udev_new();
 	if (compositor->udev == NULL) {
 		weston_log("Failed to initialize udev context.\n");