Allow bit_cast to work for 80bit long double (#4246)

include/fmt/format.h

@@ -419,17 +419,17 @@ template <> constexpr auto num_bits<uint128_fallback>() -> int { return 128; }
 // and 128-bit pointers to uint128_fallback.
 template <typename To, typename From, FMT_ENABLE_IF(sizeof(To) > sizeof(From))>
 inline auto bit_cast(const From& from) -> To {
-  constexpr auto size = static_cast<int>(sizeof(From) / sizeof(unsigned));
+  constexpr auto size = static_cast<int>(sizeof(From) / sizeof(unsigned short));
   struct data_t {
-    unsigned value[static_cast<unsigned>(size)];
+    unsigned short value[static_cast<unsigned>(size)];
   } data = bit_cast<data_t>(from);
   auto result = To();
   if (const_check(is_big_endian())) {
     for (int i = 0; i < size; ++i)
-      result = (result << num_bits<unsigned>()) | data.value[i];
+      result = (result << num_bits<unsigned short>()) | data.value[i];
   } else {
     for (int i = size - 1; i >= 0; --i)
-      result = (result << num_bits<unsigned>()) | data.value[i];
+      result = (result << num_bits<unsigned short>()) | data.value[i];
   }
   return result;
 }