Deletes an exit control block from the list of control blocks for
    the calling access mode. Exit control blocks are declared by the
    Declare Exit Handler ($DCLEXH) service and are queued according
    to access mode in a last-in first-out order.

    Format

      SYS$CANEXH  [desblk]

    C Prototype

      int sys$canexh  (void *desblk);