title: makefile using custom directory and library
body: <p>I wrote a makefile: </p>
  
  <pre><code>all: server client
  server: server.o des.o sha1.o
  /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -o server server.o des.o sha1.o -I /usr/local/include/ -lgmp 
  client: client.o des.o sha1.o
  /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -o -lgmp client client.o des.o sha1.o -I /usr/local/include/ 
  server.o: server.c
  /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -c -lgmp server.c -I /usr/local/include/
  client.o: client.c
  /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -c -lgmp client.c -I /usr/local/include/
  des.o: des.c des.h
  /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -c -lgmp des.c -I /usr/local/include/
  sha1.o: sha1.c sha1.h /usr/local/arm-2009q1/bin/arm-none-linux-gnueabi-gcc -c -lgmp sha1.c -I /usr/local/include/
  
  clean: -rm *.o server client
  </code></pre>
  
  <p>then gcc told me that cannot find -lgmp. I tried to put it in other places, there were other different errors...</p>
  
  <p>In plus, I want to know if it's possible to put 2 elements in the target.</p>