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/cpptoolssettings.h

@@ -51,7 +51,7 @@ class CPPTOOLS_EXPORT CppToolsSettings : public QObject
 
 public:
     explicit CppToolsSettings(QObject *parent);
-    ~CppToolsSettings();
+    ~CppToolsSettings() override;
 
     static CppToolsSettings *instance();