use Makefile.base for shell_commands

sys/shell/commands/Makefile

@@ -38,18 +38,5 @@ DEP = $(SRC:%.c=$(BINDIR)%.d)
 
 MODULE =shell_commands
 
-$(BINDIR)$(MODULE).a: $(OBJ)
-	$(AR) rc $(BINDIR)$(MODULE).a $(OBJ)
+include $(RIOTBASE)/Makefile.base
 
-# pull in dependency info for *existing* .o files
--include $(OBJ:.o=.d)
-
-# compile and generate dependency info
-$(BINDIR)%.o: %.c
-	$(CC) $(CFLAGS) $(INCLUDES) -c $*.c -o $(BINDIR)$*.o
-	$(CC) $(CFLAGS) $(INCLUDES) -MM $*.c > $(BINDIR)$*.d
-	@printf "$(BINDIR)"|cat - $(BINDIR)$*.d > /tmp/riot_out && mv /tmp/riot_out $(BINDIR)$*.d
-
-# remove compilation products
-clean::
-	rm -f $(BINDIR)$(MODULE).a $(OBJ) $(DEP) $(ASMOBJ)