CMakeProjectManager: Add File System virtual folder

If a CMake project cannot be parsed by CMake, it is practically unusable in
Qt Creator. According to discussion in QTCREATORBUG-24677, a virtual
folder with the project's file system view is added to the project
manager as a convenience feature.

Fixes: QTCREATORBUG-24677
Change-Id: I48775bb89c704d3f7e5bb21ec6481bd5cc0f4b6c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildsystem.h

@@ -123,11 +123,11 @@ private:
     void combineScanAndParse();
 
     std::unique_ptr<CMakeProjectNode> generateProjectTree(
-        const QList<const ProjectExplorer::FileNode *> &allFiles);
-
+        const QList<const ProjectExplorer::FileNode *> &allFiles, bool includeHeadersNode);
     void checkAndReportError(QString &errorMessage);
 
     void updateProjectData();
+    void updateFallbackProjectData();
     QList<ProjectExplorer::ExtraCompiler *> findExtraCompilers();
     void updateQmlJSCodeModel();