PiBox

The correct order, which helps with step-wise updates of component versions, is:

1. xcc
2. kernel
3. busybox
4. rpifw
5. gles
6. buildroot
7. pkg

This is arranged in config.mk, where the includes are listed.

The first three help to validate a basic boot operation works with a new toolchain. The toolchain can build a kernel to replace on a working SD card (from a previous build) in <boot>/kernel7.img. If that boots without crashes then busybox can be rebuilt and the initramfs.gz replace the one in <boot>/initramfs.gz. That will allow the boot to get as far as the old rootfs with squashfs/overlay in the initramfs. If that works, it's clear that the new toolchain CAN work though you never know what problems will be uncovered in the various user space tools in the rootfs.

Rpifw and gles are only meaningful once buildroot is done, but it can't be done until they are. So those three go together as a group.