Gets a group database entry for a group ID.
    This function is OpenVMS Alpha and Integrity servers only.
    Format
      #include  <types.h>
      #include  <grp.h>
      struct group *getgrgid  (gid_t gid);
1 – Argument
 gid
    The group ID of the group for which the group database entry is
    to be retrieved.
2 – Description
    The getgrgid function searches the group database for an entry
    with a matching gid and returns a pointer to the group structure
    containing the matching entry.
3 – Return Values
    x                  Pointer to a valid group structure containing
                       a matching entry.
    NULL               An error occurred.
                       Note: The return value points to a static area
                       that is overwritten by subsequent calls to
                       getgrent, getgrgid, or getgrnam.
                       On error, the function sets errno to one of
                       the following values:
                       o  EACCES - The user process does not have
                          appropriate privileges enabled to access
                          the user authorization file.
                       o  EIO - An I/O error has occurred.
                       o  EINTR - A signal was intercepted during
                          getgrgid.
                       o  EMFILE - OPEN_MAX file descriptors are
                          currently open in the calling process.
                       o  ENFILE - The maximum allowable number of
                          files is currently open in the system.
                       Applications checking for error situations
                       must set errno to 0 before calling getgrgid.
                       If errno is set on return, an error has
                       occurred.