Adds the signals in mask to the current set of signals being
    blocked from delivery.

    Format

      #include  <signal.h>

      int sigblock  (int mask);

1 - Argument

 mask

    The signals to be blocked.

2 - Description

    Signal i is blocked if the i - 1 bit in mask is a 1. For example,
    to add the protection-violation signal to the set of blocked
    signals, use the following line:

    sigblock(1 << (SIGBUS - 1));

    You can express signals in mnemonics (such as SIGBUS for a
    protection violation) or numbers as defined in the <signal.h>
    header file, and you can express combinations of signals by using
    the bitwise OR operator (|).

3 - Return Value

    x                  Indicates the previous set of masked signals.