This disable the rust backend on iOS until we sort it out -- the old backend
still works well.
This essentially disables all device management: enumeration, recovery after
device disappearance, etc. This also disables Aggregate device support, but it
should fall back on regular duplex IO code.
The modifications done to the backend are put in a patch applied during update,
as usual. When not building for iOS, cubeb-coreaudio-rs is still used, and is
not modified by this patch.
I'm including a small assert disabling that stems from the fact that there's no
dynamic linker and so we can't do ffts for Web Audio API yet.
Differential Revision: https://phabricator.services.mozilla.com/D205449
97496687b0