CppTools: Use override consistently

clang-tidy fixes from modernize-use-override check.

Change-Id: I0e6d6a9df3e87b8042ccc5ea0adc70070a3821d6
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/cpptools/clangdiagnosticconfigswidget.h

@@ -58,7 +58,7 @@ public:
             const ClangDiagnosticConfigsModel &diagnosticConfigsModel = ClangDiagnosticConfigsModel(),
             const Core::Id &configToSelect = Core::Id(),
             QWidget *parent = 0);
-    ~ClangDiagnosticConfigsWidget();
+    ~ClangDiagnosticConfigsWidget() override;
 
     Core::Id currentConfigId() const;
     ClangDiagnosticConfigs customConfigs() const;