Fix gcc warnings about testing undefined preprocessor symbol.

Use #ifdef instead of #if to test for __WXPALMOS[56]__.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63952 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/widgets/widgets.cpp

@@ -337,9 +337,9 @@ bool WidgetsApp::OnInit()
     title += wxT("wxMAC");
 #elif defined(__WXMOTIF__)
     title += wxT("wxMOTIF");
-#elif __WXPALMOS5__
+#elif defined(__WXPALMOS5__)
     title += wxT("wxPALMOS5");
-#elif __WXPALMOS6__
+#elif defined(__WXPALMOS6__)
     title += wxT("wxPALMOS6");
 #else
     title += wxT("wxWidgets");