DEPENDPATH merely says where to look for impliciit dependencies, not
where to find explicit ones.
fwiw, the other way round may be considered correct, but DEPENDPATH
exists for the sole purpose of limiting which paths should cause
recompilations, so it would be counterproductive to extend with with
VPATH.
Task-number: QTBUG-11912
Change-Id: I86450b5fd5aeb1f1b015b53f0adcd167ff4ce04d
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>