[Bug c/84900] Compiler report a error unexpectedly.

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84900

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Yes, I'd consider this invalid code.  Presumably there's some issue with 
the GNU extension allowing casts of structs to the same type, whereby in 
some cases it fails to make the result of the cast not an lvalue.