ClangCodeModel: Prevent outdated fix-its from getting applied

The code locations might no longer be correct.

Fixes: QTCREATORBUG-21818
Change-Id: I866a29d2fd63ff65cf33168024f7788c5f6e3547
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdiagnosticmanager.h

@@ -58,6 +58,7 @@ public:
     TextEditor::RefactorMarkers takeFixItAvailableMarkers();
 
     QList<TextEditor::TextMark *> diagnosticTextMarksAt(uint line, uint column) const;
+    bool diagnosticsInvalidated() const { return m_diagnosticsInvalidated; }
 
     void invalidateDiagnostics();
     void clearDiagnosticsWithFixIts();