The firmware for the various target microcontrollers will only be built if
suitable compilers are present.  All of these are specified in the build
dependencies *except* for the ARM Cortex targets which currently require a
bare-metal toolchain which is not yet packaged for Debian.

See http://altusmetrum.org/AltOS/building for details on how to build and
install a suitable toolchaing for ARM Cortex M0 and M3 hardware targets.
