Should a definition inside template class be instantiated if it is not used?

template <typename T>
struct A
{
    static constexpr T obj {};

    static constexpr bool noexcept_copy = noexcept( T{obj} );
    static void UsesCopy() { T{obj}; }

    static constexpr int  C = 1;
};

struct NoCopy
{
    constexpr NoCopy() = default;
    NoCopy(const NoCopy&) = delete;
};

int main()
{
    return A<NoCopy>::C;
}

The code above is successfully compiled by GCC, but Clang gives a compilation error:

tmp.cpp:6:57: error: call to deleted constructor of 'NoCopy'
        static constexpr bool noexcept_copy = noexcept( T{obj} );
                                                        ^~~~~~
tmp.cpp:20:16: note: in instantiation of template class 'A<NoCopy>' requested here
        return A<NoCopy>::C;
               ^
tmp.cpp:15:9: note: 'NoCopy' has been explicitly marked deleted here
        NoCopy(const NoCopy&) = delete;
        ^
1 error generated.

The A::UsesCopy function uses copy constructor as well, but the compiler does not complain about the usage of deleted function there. What is the difference between UsesCopy function and noexcept_copy constexpr? Both use copy constructor of NoCopy class and both are not used but the constexpr definition produces a compilation error, the function definition does not.

PS. Clang compiles the code above with -std=c++17 or -std=c++2a, but not with -std=c++11 or -std=c++14.