No, I don't think this is right. As best I can tell, there is no cap on
the size of a struct that is passed by register.
http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi/srch3@o32/0650/bks/SGI_Developer/books/Mpro_n32_ABI/sgi_html/ch02.html#id80931
I.e., o32 and n32/n64 are the same -> never pass structures by reference.
OK, patch withdrawn, I will resubmit it using this assumption,
just to get the gdbarch-ification checked in, and then we can
work on resolving how N32/64 should work.
Thanks!