USD version 21.02 includes two of the changes Blender used to patch in,
which have now been removed from usd.diff. Unfortunately 21.02
introduces another issue where LZ4 symbols are accidentally exported,
causing linker errors. Fortunately these symbols are only used for
testing, so I added a patch hunk that simply removes their extern "C"
declaration.
The LZ4 linker issue has been reported upstream at
https://github.com/PixarAnimationStudios/USD/issues/1447.