libpulseaudio doesn't currently build on darwin after a recent
upgrade (#160097). When looking closely at the darwin build, it
appeared that it wasn't being used at all.
❯ nix log $(nix-build --no-out-link channel:nixpkgs-unstable --argstr system x86_64-darwin -A qt512.qtmultimedia) | grep PulseAudio
Checking for PulseAudio >= 0.9.10... no
PulseAudio ............................. no
❯ nix log $(nix-build --no-out-link channel:nixpkgs-unstable --argstr system x86_64-darwin -A qt514.qtmultimedia) | grep PulseAudio
Checking for PulseAudio >= 0.9.10... no
PulseAudio ............................. no
❯ nix log $(nix-build --no-out-link channel:nixpkgs-unstable --argstr system x86_64-darwin -A qt515.qtmultimedia) | grep PulseAudio
Checking for PulseAudio >= 0.9.10... no
PulseAudio ............................. no
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