makefile调用其他makefile

|-- Makefile
|-- test1
||-- Makefile
||-- bin
|| `-- test
||-- hello.o
||-- include
|| `-- hello.h
| `-- src
| `-- hello.c
`-- test2
|-- Makefile
|-- bin
| `-- test
|-- hello.o
|-- include
| `-- hello.h
|-- obj
`-- src
`-- hello.c
根目录下的Makefile文件调用test2中的Makefile文件：
根目录下的Makefile文件

SUBDIR= ./test2
MAKE= make
subsystem:
cd $(SUBDIR)&& $(MAKE)

test2中的Makefile文件：

all: ./bin/test

CC= gcc
INCLUDE= ./include
vpath%.c ./src
vpath%.h ./include

./bin/test: hello.o
$(CC)-o $@ $^
hello.o: hello.c hello.h
$(CC)-c $<-I$(INCLUDE)
.PHONY: clean
clean:
-rm *.o