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.