Quite specialized build system for Qt on Raspberry Pi. Note: the image is an x86_64 image, it cross compiles for r-pi. (Hence the name baker: it's making pi images. Ha ha ha ha.)
To use this properly, you would likely need to rebuild the sysroot. It's fairly straightforward to do this, really just a few rsync calls. Best guide for that is here: https://wiki.qt.io/RaspberryPi2EGLFS
This image is building the Qt 5.9.0 libraries, minus most of the GUI parts. The initial focus was on resin/rpi-raspbian as a runtime. Some restoration work on the Qt libraries likely needed there.