Clang: add back flag indicating incomplete translation units.

This speeds up the semantic highlighting significantly.

Task-number: QTCREATORBUG-11346
Change-Id: I968f066fff7002a9cc10dd9577a750644efe026b
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/clangcodemodel/semanticmarker.cpp

@@ -67,6 +67,7 @@ void SemanticMarker::setFileName(const QString &fileName)
 
     unsigned clangOpts = clang_defaultEditingTranslationUnitOptions();
     clangOpts |= CXTranslationUnit_DetailedPreprocessingRecord;
+    clangOpts |= CXTranslationUnit_Incomplete;
     clangOpts &= ~CXTranslationUnit_CacheCompletionResults;
     m_unit->setManagementOptions(clangOpts);
 }