as mac's make might pick the one without the dependency on the direcotry
when trying to "make" that <module>.helpfiles target

Change-Id: I60a55be118bc9a41352dad94326247b02aef1dd6
Reviewed-on: https://gerrit.libreoffice.org/56960
Tested-by: Jenkins
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>