makefiles/cflags: enable C++14 by default
makefiles/cflags: enable C++14 by default


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