Deletes a specified individual signal.
    Format
      #include  <signal.h>
      int sigdelset  (sigset_t *set, int sig_number;)
1 – Arguments
 set
    The signal set.
 sig_number
    The individual signal.
2 – Description
    The sigdelset function deletes the individual signal specified by
    sig_number from the signal set specified by set.
    This function operates on data objects that you can address by
    the application, not on any set of signals known to the system.
    For example, this function does not operate on the set blocked
    from delivery to a process or the set pending for a process.
3 – Return Values
    0                  Indicates success.
    -1                 Indicates an error; errno is set to the
                       following value:
                       o  EINVAL - The value of sig_number is not a
                          valid signal number.