Which namespace does the extern declaration refer?

Question

I found an inconsistent behavior of the Q_INIT_RESOURCE() macros in Qt, where it may fail if being compiled with GCC.

Consider the code:

do {
    extern void func();
    func();
}
while(false);

Here we declare an external function and call it: so far so good. That is the approach that the macros is using under the hood. Now let's try to call this code from two different functions, one in a namespace, the other in the global namespace:

void funcGlobal() {
    do {
        extern void func();
        func();
    }
    while(false);
}

namespace ns {
void funcNamespace() {
    do {
        extern void func();
        func();
    }
    while(false);
}
}

void func() { std::cout << 1; }

namespace ns {
void func() { std::cout << 2; }
}

As I can see, MSVC calls the ::func() in both cases, but GCC calls ::func() from the global function and ns::func() from the functionNamespace. Intuitively I find MSVC more consistent, but my question is: what does the standard say, and which compiler is correct?

Regarding the macros: due to the problem above calling the macros Q_INIT_RESOURCE() from any function that is not in the global namespace causes the compiler error. I have to fix that using an additional level of indirection, wrapping the usage of the macros into a global function.