put libraries last in order to fix link error on ubuntu 14.04

Otherwise I end up with the following error:
,----
| gcc -Wall -lutil -o cp437 cp437.c
| /tmp/ccKg5S53.o: In function `main':
| cp437.c:(.text+0x40b): undefined reference to `forkpty'
| collect2: error: ld returned 1 exit status
| make: *** [cp437] Error 1
`----