The attatched tweaks structs.exp so that it KFAILs the case where a 
"return struct" fails because the target hasn't implemented the relevant 
code.

Jeff and I were puzzling over an apparent regression in the ia64 - this 
better clasifies it as something that is known to have never worked.

So, jeff, if it works for you, I'll commit it in a day or so,
Andrew