Also clean the c-common files
--- a/Makefile
+++ b/Makefile
@@ -22,6 +22,7 @@ jack-scope: jack-scope.c
 	gcc $(CFLAGS) -o jack-scope jack-scope.c $(LDLIBS) -lX11 -lXext
 
 clean:
+	(cd c-common ; make clean)
 	rm -f $(bin) *.o
 
 install: