CppTools: Auto-include pre-compiled headers

So far the pre-compiled headers were processed (thus defines from those
headers were visible), but the actual includes for the documents were
not added, which is necessary for lookup/completion.

Note that this will be only done if pre-compiled headers are not ignored
(Options > C++ > Code Model > [] Ignore pre-compiled headers).

Change-Id: I54a8e6b00597af164d958e3e9f2a1075ea187788
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/cplusplus/FastPreprocessor.h

@@ -57,7 +57,8 @@ public:
     QByteArray run(Document::Ptr newDoc, const QByteArray &source);
 
     // CPlusPlus::Client
-    virtual void sourceNeeded(unsigned line, const QString &fileName, IncludeType mode);
+    virtual void sourceNeeded(unsigned line, const QString &fileName, IncludeType mode,
+                              const QStringList &initialIncludes = QStringList());
 
     virtual void macroAdded(const Macro &);