classpath: Add file to DEPENDS

shared state exposed this build time error

| java_net_VMURLConnection.c:44:19: fatal error: magic.h: No such file or directory
| compilation terminated.
| make[3]: *** [java_net_VMURLConnection.lo] Error 1
| make[3]: *** Waiting for unfinished jobs....

classpath uses libmagic and file provides it
so add that to depends

Signed-off-by: Khem Raj <raj.khem@gmail.com>