Since having pulseaudio on target has become an option, agl-service-radio does not compile anymore if 4A is not available, either, which is the case on minimal runtime images.

Namely, the current logic in CMake is to fallback to pulseaudio backend when HAVE_4A_FRAMEWORK is not set.

Notice that fixing the build is likely not sufficient, since in the case of kingfisher radio, without 4A, the gstreamer pipeline uses a pulsesink, so it will fail at runtime if unchanged.

A needed fix would to fallback to alsa "hw:0" (assuming alsa considers it at the default playback), initializing the 'output' variable to that value instead of NULL.