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.cpp

@@ -66,9 +66,10 @@ QByteArray FastPreprocessor::run(Document::Ptr newDoc, const QByteArray &source)
     return preprocessed;
 }
 
-void FastPreprocessor::sourceNeeded(unsigned line, const QString &fileName,
-                                    IncludeType mode)
+void FastPreprocessor::sourceNeeded(unsigned line, const QString &fileName, IncludeType mode,
+                                    const QStringList &initialIncludes)
 {
+    Q_UNUSED(initialIncludes)
     Q_ASSERT(_currentDoc);
     // CHECKME: Is that cleanName needed?
     QString cleanName = QDir::cleanPath(fileName);