Add tcpdump and libpcap.

- Update the file builder generator to handle generator specific cflags and
  includes. The tcpdump and libpcap have localised headers and need specific
  headers paths to see them. There are also module specific flags and these
  need to be passed to the lex and yacc generators.

- Add the tcpdump support.

rtemsbsd/include/machine/rtems-bsd-commands.h

@@ -58,6 +58,8 @@ int rtems_bsd_command_route(int argc, char **argv);
 
 int rtems_bsd_command_dhcpcd(int argc, char **argv);
 
+int rtems_bsd_command_tcpdump(int argc, char **argv);
+
 __END_DECLS
 
 #endif /* _RTEMS_BSD_MACHINE_RTEMS_BSD_COMMANDS_H_ */