private copy ctor with user-defined assign op

[Bob Nelson]

Consider this program which compiles with no errors on GNU C++ 3.3.X
and earlier. Why does GNU C++ 3.4.X require a public copy ctor in
order to compile?

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class C {
private:
    C(const C &);
public:
    C(): i(0) {}
    C(int i): i(i) {}
    C &operator=(const C &rhs) {
        this->i = rhs.i;
        return *this;
    }
private:
    int i;
};

int main()
{
    C c;

    c  = C(42);
}
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