Function isnan

extlibs/fmt/include/fmt/chrono.h:664–666

template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline bool isnan(T) {
  return false;
}
template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
inline bool isnan(T value) {
  return std::isnan(value);