Make sure that external sitl project will be rebuild in case of sourcve has changed

src/firmware/posix/sitl_target.cmake

@@ -66,6 +66,11 @@ ExternalProject_Add(sitl_gazebo
 	)
 set_target_properties(sitl_gazebo PROPERTIES EXCLUDE_FROM_ALL TRUE)
 
+ExternalProject_Add_Step(sitl_gazebo forceconfigure
+	DEPENDEES update
+	DEPENDERS configure
+	ALWAYS 1)
+
 # create targets for each viewer/model/debugger combination
 set(viewers none jmavsim gazebo replay)
 set(debuggers none ide gdb lldb ddd valgrind callgrind)