Here's a small patch for the AllegroCL backend. Without this patch it breaks for me if I invoke, say, slime-compile-and-load-file on the following file
(defun foo (x) (bar x))
(defun quux (y) (bar y))
i.e. if there's more than one position where the undefined function is referenced. Maybe this is new in AllegroCL 7.0.
Cheers, Edi.