Only one polling mechanism is compiled

Till now wrappers for all the polling mechanisms available on
the given platform were compiled, although only one of them
was used. This patch compiles just the used one. This can
make libzmq binary more concise.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/kqueue.hpp

@@ -21,10 +21,9 @@
 #ifndef __ZMQ_KQUEUE_HPP_INCLUDED__
 #define __ZMQ_KQUEUE_HPP_INCLUDED__
 
-#include "platform.hpp"
-
-#if defined ZMQ_HAVE_FREEBSD || defined ZMQ_HAVE_OPENBSD ||\
-    defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_NETBSD
+//  poller.hpp decides which polling mechanism to use.
+#include "poller.hpp"
+#if defined ZMQ_USE_KQUEUE
 
 #include <vector>
 
@@ -96,6 +95,8 @@ namespace zmq
         const kqueue_t &operator = (const kqueue_t&);
     };
 
+    typedef kqueue_t poller_t;
+
 }
 
 #endif