C++: Preprocessor: Do not add configurationFileName() to the seen files

After processing configurationFileName() the first time, it was added to
the already seen files (m_included). Thus, on parsing further files, it
was ignored and with that all the project defines.

Task-number: QTCREATORBUG-9107
Change-Id: Ia4817dfa3b30ed27d142f7f3eeb6f099d0653441
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -514,7 +514,8 @@ void CppPreprocessor::sourceNeeded(unsigned line, const QString &fileName, Inclu
         m_currentDoc->addIncludeFile(absoluteFileName, line);
     if (m_included.contains(absoluteFileName))
         return; // we've already seen this file.
-    m_included.insert(absoluteFileName);
+    if (absoluteFileName != modelManager()->configurationFileName())
+        m_included.insert(absoluteFileName);
 
     unsigned editorRevision = 0;
     QString contents;