Assigns a condition handler address to the primary, secondary, or
    last chance exception vectors, or removes a previously assigned
    handler address from any of these three vectors.

    Format

      SYS$SETEXV  [vector] ,[addres] ,[acmode] ,[prvhnd]

    C Prototype

      int sys$setexv  (unsigned int vector, int

                      (*addres)(__unknown_params), unsigned

                      int acmode, void *(*(prvhnd)));