bpo-31904: Adapt the _signal module to VxWorks RTOS (GH-12304)

Limited signal fields in VxWorks.

Misc/NEWS.d/next/Library/2019-03-13-14-55-02.bpo-31904.834kfY.rst

+Add _signal module support for VxWorks.

Modules/signalmodule.c

@@ -1079,11 +1079,18 @@ fill_siginfo(siginfo_t *si)
 
     PyStructSequence_SET_ITEM(result, 0, PyLong_FromLong((long)(si->si_signo)));
     PyStructSequence_SET_ITEM(result, 1, PyLong_FromLong((long)(si->si_code)));
+#ifdef __VXWORKS__   
+    PyStructSequence_SET_ITEM(result, 2, PyLong_FromLong(0L));
+    PyStructSequence_SET_ITEM(result, 3, PyLong_FromLong(0L));
+    PyStructSequence_SET_ITEM(result, 4, PyLong_FromLong(0L));
+    PyStructSequence_SET_ITEM(result, 5, PyLong_FromLong(0L));
+#else   
     PyStructSequence_SET_ITEM(result, 2, PyLong_FromLong((long)(si->si_errno)));
     PyStructSequence_SET_ITEM(result, 3, PyLong_FromPid(si->si_pid));
     PyStructSequence_SET_ITEM(result, 4, _PyLong_FromUid(si->si_uid));
     PyStructSequence_SET_ITEM(result, 5,
                                 PyLong_FromLong((long)(si->si_status)));
+#endif   
 #ifdef HAVE_SIGINFO_T_SI_BAND
     PyStructSequence_SET_ITEM(result, 6, PyLong_FromLong(si->si_band));
 #else