Fix compilation in under -no-c++11 mode

IndexSetter can't be passed to QObject::connect() since C++98 templates
require global types (they can't be function-local).

Change-Id: I099322f835661d4679140b7810b50dbeb0e4b9e0
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/widgets/widgets/qcombobox.cpp

@@ -2377,6 +2377,16 @@ QSize QComboBox::sizeHint() const
 }
 
 #ifdef Q_OS_OSX
+
+namespace {
+struct IndexSetter {
+    int index;
+    QComboBox *cb;
+
+    void operator()(void) { cb->setCurrentIndex(index); }
+};
+}
+
 /*!
  * \internal
  *
@@ -2391,13 +2401,6 @@ bool QComboBoxPrivate::showNativePopup()
     if (QPlatformMenu *menu = theme->createPlatformMenu()) {
         int itemsCount = q->count();
 
-        struct IndexSetter {
-            int index;
-            QComboBox *cb;
-
-            void operator()(void) { cb->setCurrentIndex(index); }
-        };
-
         QList<QPlatformMenuItem *> items;
         items.reserve(itemsCount);
         QPlatformMenuItem *currentItem = 0;