Upgrade xz from 5.2.12 -> 5.8.1

[jjhelmus]

In version 5.6.0 and newer, liblzma is licensed under the BSD Zero Clause License (0BSD).

[jjhelmus]

On my arm64 macbook this upgrade significantly improves the performance of lzma compression in Python.

Using the pybench benchmarks from #846

With xz 5.2.12 
...
Compress using LZMA algorithm:
[========================================] 100.0% 0:00:17
...

With xz 5.8.1
...
Compress using LZMA algorithm:
[========================================] 100.0% 0:00:04
...

This performance is in line with other Python interpreters I've examined.