Segmentation fault when using xz compression

[Tong Sun]

Just like reported (twice) at https://bugzilla.redhat.com/show_bug.cgi?id=1350122,
dar will Segmentation fault when using the xz compression:

$ /usr/bin/dar -zxz -R . -c /path/to/my-dar-full
Segmentation fault

Mainly because `xz` support is actually disabled from libdar at compile time; i.e.

$ dar -V | fgrep xz
   Liblzma compression (xz) : NO

$ apt-cache policy dar
dar:
  Installed: 2.5.14+bis-1
  Candidate: 2.5.14+bis-1
  Version table:
 *** 2.5.14+bis-1 500
        500 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

$ lsb_release -rd
Description: Ubuntu 18.04 LTS
Release: 18.04