TextEditor: Fix compile with gcc 4.7.3

Change-Id: I59b401c4d7a75398fddc8f6e3a0671fc49f0cb47
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/cpptools/cppcompletionassist.cpp

@@ -86,6 +86,7 @@ public:
     CppAssistProposalItem() :
         m_isOverloaded(false) {}
 
+    ~CppAssistProposalItem() Q_DECL_NOEXCEPT {}
     bool prematurelyApplies(const QChar &c) const override;
     void applyContextualContent(TextDocumentManipulatorInterface &manipulator, int basePosition) const override;