Skip Executable_canvasdemo unless DESKTOP

For example, we don't build the vclmain library for non-DESKTOP.

Change-Id: I01a1bcd6387e86c60e5543fcb8009fd1df914a20

canvas/Module_canvas.mk

@@ -24,7 +24,8 @@ $(eval $(call gb_Module_add_targets,canvas,\
 	Library_canvastools \
 	Library_simplecanvas \
 	Library_vclcanvas \
-	$(if $(DISABLE_GUI),,Executable_canvasdemo) \
+	$(if $(filter DESKTOP,$(BUILD_TYPE)), \
+		$(if $(DISABLE_GUI),,Executable_canvasdemo)) \
 ))
 
 ifeq ($(ENABLE_CAIRO_CANVAS),TRUE)