discrepancy between clang and g++ in dealing with const objects

Consider the code:

struct Foo
{
    int x = 10;
};

int main()
{
    const Foo foo;
}

It compiles under g++ http://ift.tt/1w9NTwv, however spits an error under clang++ http://ift.tt/1xz7Un4 :

error: default initialization of an object of const type
      'const Foo' requires a user-provided default constructor

I am not sure who's right here. Why do we need a default ctor since we perform in-class initialization?