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Description of problem:
If you try to run a UML kernel on phoebe, (either a generic build (2.4.20 plus
uml patch 1) or vmlinuz-2.4.18-19.8.0uml from redhat 8.0), it quickly exits with
Kernel panic: outer trampoline didn't exit with SIGKILL
having failed an internal safety check.
The relevant bit of code generating this error is in arch/um/kernel/process.c, 

        /* Start the process and wait for it to kill itself */
        new_pid = clone(outer_tramp, (void *) sp, clone_flags, &arg);
        if(new_pid < 0) return(-errno);
        while((err = waitpid(new_pid, &status, 0) < 0) && (errno == EINTR)) ;
        if(err < 0) panic("Waiting for outer trampoline failed - errno = %d",
                          errno);
        if(!WIFSIGNALED(status) || (WTERMSIG(status) != SIGKILL))
                panic("outer trampoline didn't exit with SIGKILL");

if you hack the code a bit you find that
WIFSIGNALED(status)=1 and WTERMSIG(status)=82, which doesn't make a lot of sense
to me. There was no problem on 8.0 (vmlinuz-2.4.18-19.8.0uml worked unmodified)
and booting the main system kernel with the nosysinfo flag makes no difference.
If you disable the test altogether the uml system boots normally.

I have observed the bug with several kernel/glibc versions up to
kernel-2.4.20-2.49 and glibc-2.3.1-51

Steps to Reproduce:
1. Try to boot a uml kernel (no uml file system needed as it doesn't get that far!)