In the mean time, I figured that changing Alexandria's version from
"0.0.0-..." to "0.0.0" did the trick.

Now I'm stuck at packaging sbcl-cffi-gtk...

I'm fairly new to Common Lisp and I must say it's pretty overwhelming! :/
Any recommendation in terms of documentation to get me started?
I'll focus on the ASDF manual for now.

-- 
Pierre Neidhardt