GCC/CLang对模板模板参数的部分特化不一致

GCC和clang对此代码持不同意见.

#include 

template  typename Tpl> 
struct storage {
    using type_t = T;

    template 
    using storage_tpl = Tpl;
};

template  typename>
struct F{
    constexpr static int x = 1;
};

template 
struct F{
    constexpr static int x = 2;
};

int f() {
    using S = storage;

    static_assert(F().x == 2);

    return F().x;
}