Add qt-widgets-app unit test

Change-Id: I502075f79d4abf6bd5c0d2080b2f543116499ace
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

plugins/clangstaticanalyzer/unit-tests/qt-widgets-app/main.cpp

@@ -0,0 +1,11 @@
+#include "mainwindow.h"
+#include <QApplication>
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+    MainWindow w;
+    w.show();
+
+    return a.exec();
+}