Add cross-build

[ndim]

Add containerized linux builds for i386, armhf, and aarch64.

Modelled after the avrdude cross builds, but does not appear to work at this time.

[tintou]

You can now use the meson build system to do the cross-build:

On debian-based systems, you can generate the cross-compilation profile with meson env2mfile --debarch=aarch64 --cross -o my-cross-compilation-profile for instance and tweak it if required.

The cross-build is then simply meson setup --cross-file my-cross-compilation-profile build && meson compile -C build