GCC and Clang different behaviors on constexpr constructor

For this struct:

struct Wrapper {
    int value;

    constexpr explicit Wrapper(int v) noexcept : value(v) {}
    Wrapper(const Wrapper& that) noexcept : value(that.value) {}
};

And this function:

constexpr Wrapper makeWrapper(int v)
{
    return Wrapper(v);
}

The following code fails to compile for Clang (Apple LLVM version 7.3.0), but compiles fine for GCC (4.9+), both with -Wall -Wextra -Werror -pedantic-errors:

constexpr auto x = makeWrapper(123);

Clang complains that "non-constexpr constructor 'Wrapper' cannot be used in a constant expression." Which compiler is right?