g++: How RVO works in case that multiple translation units are involved

Firstly please take a look at the following code, which consists of 2 translation units.

--- foo.h ---

class Foo
{
public:
    Foo();
    Foo(const Foo& rhs);
    void print() const;
private:
    std::string str_;
};

Foo getFoo();

--- foo.cpp ---
#include <iostream>

Foo::Foo() : str_("hello")
{
    std::cout << "Default Ctor" << std::endl;
}

Foo::Foo(const Foo& rhs) : str_(rhs.str_)
{
    std::cout << "Copy Ctor" << std::endl;
}

void Foo:print() const
{
    std::cout << "print [" << str_ << "]" << std:endl;
}

Foo getFoo()
{
    return Foo(); // Expecting RVO
}

--- main.cpp ---
#include "foo.h"

int main()
{
    Foo foo = getFoo();
    foo.print();
}

Please be sure that foo.cpp and main.cpp are different translation units. So as per my understanding, we can say that there is no implementation details of getFoo() available in the translation unit main.o (main.cpp).

However, if we compile and execute the above, I could not see the "Copy Ctor" string which indicates that RVO works here.

It would be really appreciated if anyone of you kindly let me know how this can be achieved even if the implementation details of 'getFoo()' is not exposed to the translation unit main.o?

I conducted the above experiment by using GCC (g++) 4.4.6.