Hide setPrimary parameter on non-X11 platforms

It is already hidden in the UI, so make sure it also is gone as a
command line parameter. This follows the behaviour of the similar
sendPrimary parameter.
diff --git a/vncviewer/parameters.cxx b/vncviewer/parameters.cxx
index 8427818..e5ff4e6 100644
--- a/vncviewer/parameters.cxx
+++ b/vncviewer/parameters.cxx
@@ -124,12 +124,12 @@
 BoolParameter acceptClipboard("AcceptClipboard",
                               "Accept clipboard changes from the server",
                               true);
-BoolParameter setPrimary("SetPrimary",
-                         "Set the primary selection as well as the "
-                         "clipboard selection", true);
 BoolParameter sendClipboard("SendClipboard",
                             "Send clipboard changes to the server", true);
 #if !defined(WIN32) && !defined(__APPLE__)
+BoolParameter setPrimary("SetPrimary",
+                         "Set the primary selection as well as the "
+                         "clipboard selection", true);
 BoolParameter sendPrimary("SendPrimary",
                           "Send the primary selection to the "
                           "server as well as the clipboard selection",