[C++] Rewrite of the preprocessor.

This rewrite fixes a couple of issues with the pre-processor. It now
supports:
- macros in macro bodies
- stringification of parameters [cpp.stringize]
- the concatenation operator [cpp.concat]
- #include MACRO_HERE
- defined() inside macro bodies used in pp-conditions.

Change-Id: Ifdb78041fb6afadf44f939a4bd66ce2832b8601f
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

src/plugins/cpptools/cppcompletionassist.cpp

@@ -79,7 +79,7 @@
 using namespace CPlusPlus;
 using namespace CppEditor;
 using namespace CppTools;
-using namespace Internal;
+using namespace CppTools::Internal;
 using namespace TextEditor;
 
 namespace CppTools {