Hook to invoke when there's nothing left on the runnable threads
queue {\em and} we've got nothing to wait for. The value
returned is the exit code to report back. 

NOTE: This hook is really CONCURRENT specific, but we include
it in the way-independent libHSclib.a.

\begin{code}
#include "rtsdefs.h"

int
NoRunnableThreadsHook (void)
{
    fflush(stdout);
    fprintf(stderr, "No runnable threads!\n");
    return(EXIT_FAILURE);
}
\end{code}