ProjectExplorer: Sprinkle overrides over the code

Sprinkle overrides over code derived from classes in ProjectExplorer

Change-Id: Ia4cc25649f7dc00b0ea126d8176a59afbc5ed574
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/valgrind/valgrindengine.h

@@ -46,8 +46,8 @@ public:
     ValgrindRunControl(ProjectExplorer::RunConfiguration *runConfiguration,
                        Core::Id runMode);
 
-    bool startEngine();
-    void stopEngine();
+    bool startEngine() override;
+    void stopEngine() override;
 
     QString executable() const;