Check in samples/dll for WXUSINGDLL.

If it is set and DLL build of wx is used, emit an error, as the sample
won't work correctly in that case.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64182 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dll/wx_exe.cpp

@@ -31,6 +31,13 @@
 #include "wx/stattext.h"
 #include "wx/button.h"
 
+#ifndef __WXMSW__
+    #error "This sample is MSW-only"
+#endif
+
+#ifdef WXUSINGDLL
+    #error "This sample doesn't work with DLL build of wxWidgets"
+#endif
 
 // ----------------------------------------------------------------------------
 // GUI classes