the rationale is that postprocessing which is done by the generators (in
some cases right at the point of emitting code to the makefile) should
be abstracted inside the "medium-level" class which also does the path
resolution done by the generators.

along the way we also make minor fixes to the processing:
- we pay attention to CONFIG+=no_include_pwd
- we add the build dir as well when shadow building

Change-Id: Ib389942fdc0470e05c1aa49e3615b6ac00241662
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>