Use C++11’s override and remove virtual where applicable

Fixes warning: prefer using 'override' or (rarely) 'final' instead of
'virtual' [modernize-use-override]

Change-Id: I4b8b8ecce028dfd051fe14984b40115e92057a40
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/pathchooser.cpp

@@ -147,7 +147,7 @@ public:
         BinaryVersionToolTipEventFilter(pe->lineEdit()), m_pathChooser(pe) {}
 
 private:
-    virtual QString defaultToolTip() const
+    QString defaultToolTip() const override
         { return m_pathChooser->errorMessage(); }
 
     const PathChooser *m_pathChooser = nullptr;