I tried building the packages in that repository with the latest Sourcery Lite toolchain. BusyBox didn't compile (not that important, later versions does) and Qt had problems with DBus and OpenSSL. Disabling those made it compile though. Which toolchain did you use? Also you probably shouldn't be changing Qt's target prefix, try using -hostprefix instead. No idea how to get Qt or Glibc (from the toolchain) to install on the rootfs.
Also have you tried to access i.MX508's USB recovery mode? The device should appear on USB as a non-mass storage device if the correct signal is sent to the SoC on boot. Hopefully one of Kobo Touch's buttons will send that signal.