nanopb: add dependency for C++ files
nanopb: add dependency for C++ files

jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,kaspar030/RIOT,OTAkeys/RIOT,kYc0o/RIOT,jasonatran/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,OlegHahm/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,authmillenon/RIOT,kYc0o/RIOT,miri64/RIOT,kaspar030/RIOT,jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,authmillenon/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,miri64/RIOT,miri64/RIOT