GRBL firmware for M0 and STM32F103C8T6 ARM MC's help

I am going to build a small XY gantry for a diode laser. Laying around in my pile of controllers are Arduino’s, an Arduino board compatible Cortex M0 ARM controller and STM32F103C8T6 boards.

A quick search found some interesting GRBL builds for the M0 and STM32 boards. Of course Paul deGroot’s STM32 build looks like the best but I am curious if there are any current M0 compatible GRBL builds because the board I have can use an Arduino CNC shield.

All of this is for educational purposes and of course all input is welcome.