Add virtual destructor to QAxScriptSite.

Silence warning by MinGW:
qtactiveqt\src\activeqt\container\qaxscript.cpp:143: warning: deleting object of polymorphic class type 'QAxScriptSite' which has non-virtual destructor might cause undefined behavior [-Wdelete-non-virtual-dtor]

Task-number: QTBUG-45022
Change-Id: I5f221a953e44c3977ba633b999223fd4aa014666
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

src/activeqt/container/qaxscript.cpp

@@ -91,6 +91,7 @@ class QAxScriptSite : public IActiveScriptSite, public IActiveScriptSiteWindow
 {
 public:
     QAxScriptSite(QAxScript *script);
+    virtual ~QAxScriptSite() {}
 
     ULONG WINAPI AddRef();
     ULONG WINAPI Release();