Add a part about .o to the Makefile

Makefile

@@ -12,6 +12,9 @@ test.o: test.c
 fx_s2308_double.o: fx_s2308_double.c 
 	$(CC) $(CFLAGS) fx_s2308_double.c
 
+fx_s2308_longlong.o: fx_s2308_longlong.c
+	$(CC) $(CFLAGS) fx_s2308_longlong.c
+
 clean:
 	- rm $(OBJS)
 	rm fx_s2308_double