Allows a process to establish or to change its own process name.
    Format
      SYS$SETPRN  [prcnam]
    C Prototype
      int sys$setprn  (void *prcnam);
1 – Argument
 prcnam
    OpenVMS usage:process_name
    type:         character-coded text string
    access:       read only
    mechanism:    by descriptor-fixed-length string descriptor
    Process name to be given to the calling process. The prcnam
    argument is the address of a character string descriptor pointing
    to a 1- to 15-character process name string. If you do not
    specify prcnam, the calling process is given no name.