Some changes we use at ITA (minus XCVB support)

Use internal ASDF system names findable by ASDF3 (still not by ASDF2).

Also, introduce a system cl-unicode/base so files are owned by a single system
(which avoids confusing other system automation tools).

Also, use an eval-when around functions used at macro-expansion time.

PS: are you interested by the XCVB support?