Without pcm, firefox will crash with this error when playing sound
```
parts/firefox/firefox: relocation error:
/srv/slapgrid/slappart11/srv/runner/software/88ef27d24c6e0a792f72f568146a3838/parts/firefox/libxul.so:
symbol snd_pcm_open, version ALSA_0.9 not defined in file libasound.so.2 with link time reference
```
libasound.so does not contain this symbol if built with --disable-pcm