Clang: Gray out diagnostics on document change

When reparses take a while, this is helpful.

Change-Id: Ie2003a3d65b30d944d20fa19dd4161412182851c
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/baseeditordocumentprocessor.cpp

@@ -87,6 +87,10 @@ void BaseEditorDocumentProcessor::editorDocumentTimerRestarted()
 {
 }
 
+void BaseEditorDocumentProcessor::invalidateDiagnostics()
+{
+}
+
 void BaseEditorDocumentProcessor::setParserConfig(
         const BaseEditorDocumentParser::Configuration config)
 {