Are unused friend functions compiled or not?

Consider the code:
-----------------
template <class T>
struct addable2
{
   friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
};

template<class T>
struct addable : addable2<T>
{
};

template <class T>
class point : addable< point<T> >
{
};

int main()
{
   point<int> ppp;
   return 0;
}
-------------------
operator+ has a semantic error in it, there is no += operation defined
for point<int>. So should an error be issued or not?

The Standard 14.5.3-3 says:

3. When a function is defined in a friend function declaration in a
class template, the function is defined when
the class template is first instantiated. The function is defined even
if it is never used. [Note: if the function
definition is illformed
for a given specialization of the enclosing class template, the program
is illformed even if the function is never used. -end note]

This came about from trying to compile Boost code with Digital Mars C++.
Evidently, such code is common in Boost. But I feel that DMC++ correctly
rejects the code.

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