explicitly declare the module master header

we are delegating to the axbase module, but the master header generation
does not resolve transitive deps, so we need this crutch.

Task-number: QTBUG-41892
Change-Id: Ief7e8c4bde6fbea7ce6503f67d3b9d5787e09007
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>