Default destructor nothrow

The following code doesn't compile under gcc-4.7.1 but compile under clang-3.2. Which one follows the C++11 standard?

struct X {
  virtual ~X() = default;
};

struct Y : X {
  virtual ~Y() = default;
};

gcc-4.7.1 complains that:

looser throw specifier for 'virtual Y::~Y()'
error: overriding 'virtual X::~X() noexcept(true)'

Obviously, gcc-4.7.1 thinks X's default destructor nothrow, but Y's default destructor is not nothrow. Why is this? Can anyone refer to the correct place in standard? Thanks.

I saw similar questions on stackoverflow, but I didn't see the answers refering to the standard.