Change build command to work with free functions

Since the driver.cc and the $(CLASSNAME).cc both are source files and driver.cc includes
$(CLASSNME).cc a linker error is created when building and linking both of them.
If only driver.cc is built and linked everything is ok. However if there is a change in
$(CLASSNAME).cc the rebuilt has to be done. Therefore the remaining implicit rules have to stay in
the Makefile.