[PPRZ CENTER] Fixed detection of child processes exitting on Mac OS.

We are now checking if the input channel is empty when receiving the IN
callback. If that is the case we assume that the child process exitted,
ond call the close process callback that normally is treggered by the
HUP callback.

Some background: On OS X glib is using it's own implementation of poll
that does not generate the HUP signal. (It would be possible to add this
functionality modelled after the SSH implementation of bsd_poll) The
glib implementation does generate IN signal when the pipe get's closed.
So we can just check if the input channel is empty and if that is the
case infer that the pipe got closed.
[release] v5.0.3 stable version

- fix Paparazzi Center on Mac OS (detection of child processes exitting)
  [#290] (https://github.com/paparazzi/paparazzi/issues/290)
- state interface: fix stateCalcHorizontalSpeedNorm_i
- fix/improve dependency generation for building firmware
- abort with meaningful error if ARM toolchain is not found
[tests] fix perl script compile_all_test_targets

Firmwares with only a single target were not built before.
Thanks for the fix Alexandre.
[conf] remove outdated tiny2_chimu_spi airframe from tests file