CMake: Do not crash when cloning cmake buildconfigurations

Change-Id: I832981cdea16ab058f92758c9bae9b64b904d573
Task-number: QTCREATORBUG-15926
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.h

@@ -92,6 +92,7 @@ protected:
     bool fromMap(const QVariantMap &map) override;
 
 private:
+    void ctor();
     QList<ConfigModel::DataItem> completeCMakeConfiguration() const;
     void setCurrentCMakeConfiguration(const QList<ConfigModel::DataItem> &items);