Log Message:
firefox60: Add sun audio backend and make it a default where supported.

This replaces the OSS backend with something that passes the unit tests,
supports additional channels, and supports recording. It will be included
with future versions of Firefox.

Tested with:

* YouTube audio-video sync test
* about:support device detection
* WebRTC microphone recording (using an USB microphone)

While here, fix WebRTC builds.

Note: you can select an audio backend using the about:config variable
media.cubeb.backend. This can be set to options such as sun/pulse/oss.

Let me know if you still need to use the oss backend. It's very
incomplete, buggy, and FreeBSD has already removed it - ideally we
should eventually.

Bump PKGREVISION.