Had give it a try but don't think it is possible unless you had fixed number of friend. Easy solution will be like hurricane suggest used programming to loop thru it.

If you are using PL/SQL (Oracle) then you can create a function which will return concatenated friends name as a string and used it in your query.

Edited---
This SQL will return what you want but fixed friends
SELECT DISTINCT t.name, f1.friend & ', ' & f2.friend AS friends
FROM tb t, tb f1, tb f2
WHERE t.name = f1.name AND tname = f2.name
AND f1.friend < f2.friend;