The new HomePod (AudioAccessory1,1) OTA which Apple released (for whatever reason) is slightly incompatible with my old pbzx implementation due to quite a few uncompressed (16M) blocks they have in the middle of the XZ stream. I normally handled this with a shell script, but figured I can just integrate xz-devel's lzma decompressor directly. So here it is. You won't need to run xz manually anymore (though you will need liblzma, which you can easily get). This has been tested on all OTA updates (iOS/WatchOS/TvOS/PodOS/MacOS), but if something doesn't work for you, TELL ME.
Because lzma's not my source, I added my mods there with an #ifndef NOJ.
This works on MacOS and Linux. Sources will compile if you have liblzma (https://tukaani.org/xz/, or the Linux xz-devel package).