CppTools: Avoid self-include

...in CPlusPlus::Document due to cyclic includes.

Task-number: QTCREATORBUG-11457
Change-Id: I1ca19c901c26d9984d795a61879dd6b41c57096c
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpppreprocessor.cpp

@@ -355,7 +355,7 @@ void CppPreprocessor::mergeEnvironment(Document::Ptr doc)
 
         if (Document::Ptr includedDoc = m_snapshot.document(includedFile))
             mergeEnvironment(includedDoc);
-        else
+        else if (!m_included.contains(includedFile))
             run(includedFile);
     }