[ extracted from http://bugs.debian.org/195468 ]

g++ fails to recognize the ill-formed-ness of
at least the following cases, happily succeeds compiling them...:

struct foo {
  virtual void f(void);
};

struct bar {
  bar (); // user defined default constructor
};

struct doo {
  bar m_bar; // non-POD member w/ u.d.d.c
};

struct zoo: public bar { }; // inherited u.d.d.c

const foo a_foo; // ill-formed - foo has no user-declared def-cons
const bar a_bar; // ok
const doo a_doo; // ill-formed - doo has no user-declared def-cons
const zoo a_zoo; // ill-formed? not sure about this one...