This has been solved in a different way in
df5653adcbd1f9799f810f46d514b2ca4112af97.

Concerning the updates to libpng etc, they cause the rebuild of a lot of
packages, therefore they are done on the core-updates branch instead of
master. So i'm closing this issue, and if you want to update libpng etc,
please open a new issue with patches based on the core-updates branch.