If an atomic specialization has one of the following overloads,
then that overload participates in overload resolution
even if
atomic<T>::is_always_lock_free is
false:
void store(T desired, memory_order order = memory_order::seq_cst) volatile noexcept;
T operator=(T desired) volatile noexcept;
T load(memory_order order = memory_order::seq_cst) const volatile noexcept;
operator T() const volatile noexcept;
T exchange(T desired, memory_order order = memory_order::seq_cst) volatile noexcept;
bool compare_exchange_weak(T& expected, T desired,
memory_order success, memory_order failure) volatile noexcept;
bool compare_exchange_strong(T& expected, T desired,
memory_order success, memory_order failure) volatile noexcept;
bool compare_exchange_weak(T& expected, T desired,
memory_order order = memory_order::seq_cst) volatile noexcept;
bool compare_exchange_strong(T& expected, T desired,
memory_order order = memory_order::seq_cst) volatile noexcept;
T fetch_key(T operand, memory_order order = memory_order::seq_cst) volatile noexcept;
T operator op=(T operand) volatile noexcept;
T* fetch_key(ptrdiff_t operand, memory_order order = memory_order::seq_cst) volatile noexcept;