OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    Longword condition value. In most cases, the routine returns
    either the same signal passed to it in the condition value
    argument, or the return value of LIB$SIGNAL. If the routine
    fails, it signals TPU$_FAILURE and returns control to the caller.