DYN_SNDFILE=NO and DYN_MPG123=NO were ignored while DYN_FLUIDSYNTH=NO broke compilation These options should be applied to ZMusic target instead of the main executable As a bonus, it's now possible to build GZDoom without FluidSynth
In this case it was the song terminating the stream, with the new setup the main music code has to do this itself.
What's left is the CD-Audio playback and some global functions.