[feature request] preprocessor define in config (or on command line directly)

[i-make-robots]

Thank you for your great work on arduino-cli. I really appreciate all your time & energy.

I would like to feed arduino-cli a matrix of AVR types and machine styles to test them all, automatically, in a Github Action.
I have https://github.com/MarginallyClever/Makelangelo-firmware/edit/master/.github/workflows/main.yml
Many AVRs, many kinematic models run by one firmware.
kinematic models are decided with a preprocessor directive. for instance,

#define MACHINE_STYLE = POLARGRAPH

Please! In a perfect world I would like to call

arduino-cli compile --fqbn arduino:avr:mega ./Makelangelo-firmware.ino --define MACHINE_STYLE = POLARGRAPH

If this is already possible I do apologize, I was unable to find the documentation.

[obra]

#846 and #1044 are at least related.

extra_flags and --build-property may give you the rope you need.

[per1234]

Closing as duplicate of #159

[i-make-robots]

Oh awesome. I didn't find the documentation for this (fairly new) feature. Sorry to bother. Stay Excellent!

[i-make-robots]

I have moved to platformio where it would be -DROBOT_POLARGRAPH -DBOARD_RUMBA.