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/PreprocessorClient.h

@@ -32,7 +32,7 @@
 
 #include <cplusplus/CPlusPlusForwardDeclarations.h>
 
-#include <QString>
+#include <QStringList>
 #include <QVector>
 
 QT_BEGIN_NAMESPACE
@@ -100,7 +100,8 @@ public:
   virtual void startSkippingBlocks(unsigned utf16charsOffset) = 0;
   virtual void stopSkippingBlocks(unsigned utf16charsOffset) = 0;
 
-  virtual void sourceNeeded(unsigned line, const QString &fileName, IncludeType mode) = 0;
+  virtual void sourceNeeded(unsigned line, const QString &fileName, IncludeType mode,
+                            const QStringList &initialIncludes = QStringList()) = 0;
 
   static inline bool isInjectedFile(const QString &fileName)
   {