[perl #88748] [BUG] Rakudo doesn't give a good indication of what's happened when an undeclared type is used in a 'when' clause

[Christian Bartolomaeus via RT]

As it was noted recently, Rakudo now gives the same error message as STD.

I added a test to S32-exceptions/misc.t with the following commit: 
https://github.com/perl6/roast/commit/7396503e24 and I'm closing the ticket.