compile_commands: Don't produce duplicate -c arguments
compile_commands: Don't produce duplicate -c arguments

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