Unable to run prepare_port for "libc" target

[Timo Nicolai]

Hello,

I'm trying to run Genode for the first time and I've noticed that the 
prepare_port script seems to fail for the "libc" target on the current 
master branch. I'm getting:

libc  extract src.txz (libc)
xz: (stdin): File format not recognized
tar: Child returned status 1
tar: Error is not recoverable: exiting now

Hard to see what the actual issue here is, I have xz version 5.2.5 
installed if that helps.

Best regards,
Timo Nicolai