Clang: Add Symbol Indexing

It is a first step and now a database is generated if you start QtCreator.
Some code is now shared with the PchManager which can be improved in the
future.

Change-Id: Ic267fe7960f6c455d91832859a673ce98f269aa2
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangrefactoringbackend/source/symbolscollectorinterface.h

@@ -28,6 +28,8 @@
 #include "symbolentry.h"
 #include "sourcelocationentry.h"
 
+#include <filecontainerv2.h>
+
 #include <utils/smallstringvector.h>
 
 #include <string>
@@ -41,6 +43,8 @@ public:
     virtual void addFiles(const Utils::PathStringVector &filePaths,
                           const Utils::SmallStringVector &arguments) = 0;
 
+    virtual void addUnsavedFiles(const V2::FileContainers &unsavedFiles) = 0;
+
     virtual void collectSymbols() = 0;
 
     virtual const SymbolEntries &symbols() const = 0;