Update configure scripts so that ALSA, JACK and other tier-3 backends require --disable-content-sandbox as appropriate to make them work.

Currently, ALSA is probably (I haven't tried it) working for direct hardware access (and maybe also dmix?) via bug 1309098 which allows opening the audio devices (ifdef'ed). That part of ALSA seems likely to continue working under sandboxing for a while. But the ALSA framework supports plugins, which may or may not work – especially the ones that are adapters to other sound systems. JACK I know much less about, but once PulseAudio leaves the content process we're finally going to start restricting networking/sockets access (and miscellaneous other things we've had to allow to keep PA working), and that seems likely to impact other sound servers.

Mass change P3->P4 to align with new Mozilla triage process.