I’m fairly certain Yii doesn’t provide a solution for a table with 3 FKs (and I don’t even know what it would look like – aside from very intriguing!)
What you could do of course is regard table_abc as multiple MANY_MANY tables in one, meaning you can have
a MANY_MANY b
a MANY_MANY c
b MANY_MANY a
b MANY_MANY c
c MANY_MANY a
c MANY_MANY b
Although this sounds rather tricky to manage. If there is a way to solve your problem using a default database structure I’d seriously consider using it; this sounds like a major headache waiting to happen.