cmake: allow disabling pulse and alsa on linux
cmake: allow disabling pulse and alsa on linux

Since https://github.com/clangen/musikcube/pull/421 I can use pipewire
directly, which itself interfaces with ALSA and replaces pulseaudio.
Allow dropping both at build time, previously they were hard-selected
when on Linux.

Signed-off-by: Robert Günzler <4dc7c9ec434ed06502767136789763ec11d2c4b7@gnzler.io>

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