[Bug c++/28107] Incomplete type in struct added to global namespace

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28107

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, this is invalid, a member definition such as "union B b;" does not declare
a nested type, that would be:

struct A {
    union B;
    B b;
};