Name resolution works in 4.5, not 4.7 & clang

declare.cc

extern const char * const foo = "hello world\n";

main.cc

#include <stdio.h>

namespace SN {
   void fn();
}

void SN::fn() {
   extern const char * const foo;
   printf("%s", foo);
}

int main() {
   SN::fn();
   return 0;
}

Makefile

main: declare.o main.o

declare.o: declare.cc

main.o: main.cc