There's a merged pull request on the void-packages repository

qt: cross targets for ppc64, qt-webkit: fix build + ppc adjustments
https://github.com/void-linux/void-packages/pull/11497
Description: These are the necessary changes for qt4 and qt4 webkit on ppc64.

Python is newly required for qt-webkit hostmakedepends, because a python script is run during build and this script must be run with python2 (registered as python in alternatives). Some change in a host dependency switched the python version to 3, which now breaks it.