So, if you have access to an old raspberry pi, that would be the easiest way to build it for your target (armhf) architecture.
Another option is to use qemu virtualisation.
I don't think we have something like that, but maybe we can use the piece of hardware we're using that hosts our homemade OS in the same way. I'll try to ask a coworker. If all else fails, it's qemu time to emulate a raspberry PI, right ?
Okay, but then that's maybe not a question for this forum. If you are going to cross-compile for an embedded device, that's quite a specialised discipline... I can try to compile oat++ on my lime2 this afternoon (which is 32 bit arm), but that one runs a full debian distro.
All I should need is the two static library files so maybe just doing that on that debian distribution could work.