#169 WCONTINUED not defined on Hurd

[Thomas Preud'homme]

WCONTINUED and WIFCONTINUED are Linux-specific macros to the wait system call. Thus, these macros might not be defined for other operating systems such as Hurd. Yet they are used unconditionally in src/external_lookup.c

I attach to this bug report a patch that define WCONTINUED and WIFCONTINUED when not defined so that the case of a child process receiving a SIGCONT is simply not notified when these macros are not defined on the given system.