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>

tests/auto/cplusplus/preprocessor/tst_preprocessor.cpp

@@ -159,8 +159,10 @@ public:
     virtual void stopSkippingBlocks(unsigned utf16charsOffset)
     { m_skippedBlocks.last().end = utf16charsOffset; }
 
-    virtual void sourceNeeded(unsigned line, const QString &includedFileName, IncludeType mode)
+    virtual void sourceNeeded(unsigned line, const QString &includedFileName, IncludeType mode,
+                              const QStringList &initialIncludes = QStringList())
     {
+        Q_UNUSED(initialIncludes)
 #if 1
         m_recordedIncludes.append(Include(includedFileName, mode, line));
         Q_UNUSED(m_env);