(Alpha and I64 only.) The Call Routine with General Argument
    List routine calls a routine with an argument list specified
    as an array of quadwords, the first of which is a count of the
    remaining quadwords.

    Format

      LIB$CALLG_64  argument-list ,user-procedure

1 - Returns

    OpenVMS usage:quadword_unsigned
    type:         quadword (unsigned)
    access:       write only
    mechanism:    by value

    Return value, if any, of the called routine, unchanged by
    LIB$CALLG_64.

2 - Arguments

 argument-list

    OpenVMS usage:arg_list
    type:         unspecified
    access:       read only
    mechanism:    by reference, array reference

    Argument list to be passed to user-procedure. The argument-
    list argument is the address of an array of quadwords that is
    the argument list. The first quadword contains the count of the
    remaining quadwords, to a maximum of 255.

 user-procedure

    OpenVMS usage:procedure
    type:         procedure value
    access:       function call (before return)
    mechanism:    by value

    Routine that LIB$CALLG_64 calls with the specified argument list.