OSX: make tioslectors test green

lib/pure/ioselects/ioselectors_kqueue.nim

@@ -567,8 +567,11 @@ proc selectInto*[T](s: Selector[T], timeout: int,
         doAssert(true, "Unsupported kqueue filter in the queue!")
 
       if (kevent.flags and EV_EOF) != 0:
+        # TODO this error handling needs to be rethought.
+        # `fflags` can sometimes be `0x80000000` and thus we use 'cast'
+        # here:
         if kevent.fflags != 0:
-          rkey.errorCode = kevent.fflags.OSErrorCode
+          rkey.errorCode = cast[OSErrorCode](kevent.fflags)
         else:
           # This assumes we are dealing with sockets.
           # TODO: For future-proofing it might be a good idea to give the