Function const_check

extlibs/fmt/include/fmt/core.h:277–277

// A helper function to suppress bogus "conditional expression is constant"
// warnings.
template <typename T> FMT_CONSTEXPR T const_check(T value) { return value; }

// A workaround for gcc 4.8 to make void_t work in a SFINAE context.
template <typename... Ts> struct void_t_impl { using type = void; };