Windows: Fix stepping through Qt sources.

Build paths of Qt 5.2 changed.

Task-number: QTCREATORBUG-11233
Change-Id: I9e3b2d53cb10f09bc1b9d780669ebb72c595ad4f
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>