Move socket_base.hpp and err.hpp after poll.h include

These two headers also include zmq.h somewhere in their dependency
chain, so must be included after poll.h is included for builds to work
on AIX.

src/proxy.cpp

@@ -21,9 +21,7 @@
 #include <stddef.h>
 #include "platform.hpp"
 #include "proxy.hpp"
-#include "socket_base.hpp"
 #include "likely.hpp"
-#include "err.hpp"
 
 #if defined ZMQ_FORCE_SELECT
 #define ZMQ_POLL_BASED_ON_SELECT
@@ -48,6 +46,11 @@
 #include <poll.h>
 #endif
 
+// These headers end up pulling in zmq.h somewhere in their include
+// dependency chain
+#include "socket_base.hpp"
+#include "err.hpp"
+
 // zmq.h must be included *after* poll.h for AIX to build properly
 #include "../include/zmq.h"