tar behaves differently on macOS

[secretfader]

This project began life as a Linux-only implementation, but macOS is a desirable fast-follow as many developers use Apple laptops.

Unfortunately, macOS' implementation of tar (bsdtar) doesn't seem to work the same when decompressing .tar.xz archives.

System Report

macOS Catalina 10.15.3, Darwin 19.3.0

Tasks

• Correct unpacking and compilation on OS-X targets
• Setup macOS CI to prevent this bug in the future