Calls the System V IPC function msgctl(2). You'll probably have to say
first to get the correct constant definitions. If CMD is
IPC_STAT, then ARG must be a variable that will hold the returned
msqid_ds structure. Returns like
ioctl: the undefined value for error,
"0 but true" for zero, or the actual return value otherwise. See also "SysV IPC" in perlipc and the documentation for
Portability issues: "msgctl" in perlport.