The following Vala-code:
  Posix.sigset_t sigSet = new Posix.sigset_t();
  Posix.sigemptyset(sigSet);
  Posix.sigaddset(sigSet, Posix.SIGPIPE);
  Posix.sigset_t oldSet = new Posix.sigset_t();
  Posix.sigprocmask(Posix.SIG_SETMASK, sigSet, oldSet);

Is converted into the following C-code:
  sigset_t sigSet = {0};
  sigset_t _tmp18_;
  sigset_t _tmp19_;
  sigset_t oldSet = {0};
  sigset_t _tmp20_;
  sigset_t _tmp21_;
  ...
  memset (&sigSet, 0, sizeof (sigset_t));
  _tmp18_ = sigSet;
  sigemptyset (&_tmp18_);
  _tmp19_ = sigSet;
  sigaddset (&_tmp19_, SIGPIPE);
  memset (&oldSet, 0, sizeof (sigset_t));
  _tmp20_ = sigSet;
  _tmp21_ = oldSet;
  sigprocmask (SIG_SETMASK, &_tmp20_, &_tmp21_);

Problem: the mask which is given to sigprocmask() is always empty. Instead, the argument to sigaddset() and sigemptyset() may be better a reference.