ClangFormat: Fix compile with older gcc and MSVC

Amends 2d8ce380c9.

Change-Id: I44e7079ae40550e4d80a1717d4803d6864af99eb
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangformat/clangformatconfigwidget.cpp

@@ -118,7 +118,7 @@ void ClangFormatConfigWidget::connectChecks()
         auto comboBox = qobject_cast<QComboBox *>(child);
         if (comboBox != nullptr) {
             connect(comboBox,
-                    qOverload<int>(&QComboBox::currentIndexChanged),
+                    QOverload<int>::of(&QComboBox::currentIndexChanged),
                     this,
                     &ClangFormatConfigWidget::onTableChanged);
             comboBox->installEventFilter(this);