C++11 nullptr constexpr problem (Example from Chandler Carruth's speech on GoingNative 2012)

nullptr_constexpr.cpp

#include <iostream>
struct S { int n; };
struct X { X(int) {} };
void f(void*) {
  std::cerr << "Pointer!\n";
}
void f(X) {
 std::cerr << "X!\n";
}
int main() {
  f(S().n);
}

eien@eien-ubuntu:/dev/dev$ clang++ -std=c++11 problem.cpp
eien@eien-ubuntu:/dev/dev$ ./a.out
Pointer!
eien@eien-ubuntu:/dev/dev$ clang++ -std=c++03 problem.cpp -o a03
eien@eien-ubuntu:/dev/dev$ ./a03
X!