If func is the constant SIG_DFL, the action for the given
    signal is reset to the default action, which is to terminate
    the receiving process. If the argument is SIG_IGN, the signal is
    ignored. Not all signals can be ignored.

    If func is neither SIG_DFL nor SIG_IGN, it specifies the address
    of a signal-handling function. When the signal is raised, the
    addressed function is called with sig as its argument. When the
    addressed function returns, the interrupted process continues
    at the point of interruption. (This is called catching a signal.
    Signals are reset to SIG_DFL after they are intercepted, except
    as shown in the Error and Signal Handling chapter of the HP C RTL
    Reference Manual.

    You must call the signal function each time you want to catch a
    signal.

    See the "Error and Signal Handling" chapter of the HP C RTL
    Reference Manual for more information on signal handling.

    To cause an OpenVMS exception or a signal to generate a UNIX
    style signal, OpenVMS condition handlers must return SS$_RESIGNAL
    upon receiving any exception that they do not want to handle.
    Returning SS$_CONTINUE prevents the correct generation of a UNIX
    style signal.