CONTRIB: debug: address "poll" utility build on non-linux platforms

MSG_NOSIGNAL and MSG_MORE are not defined everywhere, let's make them
zero when not defined. It will roughly result in the same behavior,
albeit a bit less optimal, which is no big deal when debugging. This
should fix issue #1014.

contrib/debug/poll.c

@@ -17,6 +17,13 @@
 #define POLLRDHUP 0
 #endif
 
+#ifndef MSG_NOSIGNAL
+#define MSG_NOSIGNAL 0
+#endif
+#ifndef MSG_MORE
+#define MSG_MORE 0
+#endif
+
 int verbose = 0;
 int cmd = 0;
 int cmdstep = 0;