Clang: Make ClangAssistProposalModel members private

Change-Id: Ib8089f4afdb72840d97e5286d8be631387e4d2c5
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/clangcodemodel/clangassistproposalmodel.h

@@ -49,6 +49,9 @@ public:
 
     bool isSortable(const QString &prefix) const override;
 
+    static bool replaceDotForArrow(IAssistProposalModel *model);
+
+private:
     bool m_sortable;
     unsigned m_completionOperator;
     bool m_replaceDotForArrow;