Problem: 4.2.0 won't compile on AIX 7.1

Solution: restore inclusion of poll.h if using poll before zmq.h as
it was originally, as AIX redefines the POSIX structures and provides
compatibility macros.
Also add alternative aliases for 32 bit AIX's pollitem struct:
  events -> reqevents
  revents -> rtnevents

src/proxy.cpp

@@ -27,17 +27,23 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+//  On AIX platform, poll.h has to be included first to get consistent
+//  definition of pollfd structure (AIX uses 'reqevents' and 'retnevents'
+//  instead of 'events' and 'revents' and defines macros to map from POSIX-y
+//  names to AIX-specific names).
+//  zmq.h must be included *after* poll.h for AIX to build properly.
+//  precompiled.hpp includes include/zmq.h
+#if defined ZMQ_POLL_BASED_ON_POLL && defined ZMQ_HAVE_AIX
+#include <poll.h>
+#endif
+
 #include "precompiled.hpp"
 #include <stddef.h>
 #include "poller.hpp"
 #include "proxy.hpp"
 #include "likely.hpp"
 
-//  On AIX platform, poll.h has to be included first to get consistent
-//  definition of pollfd structure (AIX uses 'reqevents' and 'retnevents'
-//  instead of 'events' and 'revents' and defines macros to map from POSIX-y
-//  names to AIX-specific names).
-#if defined ZMQ_POLL_BASED_ON_POLL && !defined ZMQ_HAVE_WINDOWS
+#if defined ZMQ_POLL_BASED_ON_POLL && !defined ZMQ_HAVE_WINDOWS && !defined ZMQ_HAVE_AIX
 #include <poll.h>
 #endif
 
@@ -46,10 +52,6 @@
 #include "socket_base.hpp"
 #include "err.hpp"
 
-// TODO: determine if this is an issue, since zmq.h is being loaded from pch.
-// zmq.h must be included *after* poll.h for AIX to build properly
-//#include "../include/zmq.h"
-
 int capture(
         class zmq::socket_base_t *capture_,
         zmq::msg_t& msg_,