Diamond-inheritance scenario compiles fine in G++, but produces warnings/errors in VC++/Eclipse

I have a base class 'Base', which is a pure virtual class:

class Base {

public:
    virtual void A() = 0;
    virtual void B() = 0;

    virtual ~Base() { } // Eclipse complains that a class with virtual members must have virtual destructor
};

I also have 2 other classes, one of them implements A() and the other one implements B():

class DerivedA : public virtual Base
{
public:
    virtual void A() {
        printf("Hello from A");
    }
};

class DerivedB : public virtual Base
{
public:
    virtual void B() {
        printf("Hello from B");
    }
};

The virtual keyword in the declaration should solve the diamond problem.

Now I would like to combine the two classes into another class, so that both A() and B() are implemented, like this:

class DerivedC: public DerivedA, public DerivedB {
     // Now DerivedA and DerivedB are combined
};

// Somewhere else in the code
DerivedC c;
c.A();
c.B();

The problem: Even though G++ compiles the code just fine, Eclipse gives an error: The type 'DerivedC' must implement the inherited pure virtual method 'Base::B'. When compiling with visual studio, I get 2 warnings:

warning C4250: 'DerivedC' : inherits 'DerivedB::DerivedB::B' via dominance
warning C4250: 'DerivedC' : inherits 'DerivedA::DerivedA::A' via dominance

So the question is: what is the correct way of doing this? Does the code above produce undefined behavior?

Note: The title may be a little misleading, I have no idea what a good title for this question would be.