add pollset poller in AIX

add a new poller named pollset which will get benefit of performance in AIX platform.

src/poller.hpp

@@ -30,14 +30,16 @@
 #ifndef __ZMQ_POLLER_HPP_INCLUDED__
 #define __ZMQ_POLLER_HPP_INCLUDED__
 
-#if   defined ZMQ_USE_KQUEUE  + defined ZMQ_USE_EPOLL \
-    + defined ZMQ_USE_DEVPOLL + defined ZMQ_USE_POLL  \
-    + defined ZMQ_USE_SELECT > 1
+#if   defined ZMQ_USE_KQUEUE + defined ZMQ_USE_POLLSET \
+    + defined ZMQ_USE_EPOLL  + defined ZMQ_USE_DEVPOLL \
+    + defined ZMQ_USE_POLL   + defined ZMQ_USE_SELECT > 1
 #error More than one of the ZMQ_USE_* macros defined
 #endif
 
 #if defined ZMQ_USE_KQUEUE
 #   include "kqueue.hpp"
+#elif defined ZMQ_USE_POLLSET
+#    include "pollset.hpp"
 #elif defined ZMQ_USE_EPOLL
 #   include "epoll.hpp"
 #elif defined ZMQ_USE_DEVPOLL