CppTools: Check if project has changed before reparsing

This introduces an API change for the project managers. Those are not
expected to call updateSourceFiles() anymore.

Task-number: QTCREATORBUG-9581
Change-Id: I77befd29fb851c9acf87204d571da00183c9cd05
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/autotoolsprojectmanager/autotoolsproject.cpp

@@ -433,8 +433,6 @@ void AutotoolsProject::updateCppCodeModel()
     pinfo.appendProjectPart(part);
 
     modelManager->updateProjectInfo(pinfo);
-    modelManager->updateSourceFiles(m_files,
-                                    CppTools::CppModelManagerInterface::ForcedProgressNotification);
 
     setProjectLanguage(ProjectExplorer::Constants::LANG_CXX, !part->files.isEmpty());
 }