message: Fix compilation failure on Windows builds
  A previous change introduced usage of "terse static_assert" which is a C++17
  feature. Windows builds do not support this extension.
diff: @@ -369,8 +369,9 @@ inline PendingCounts::Handle PendingCounts::Layout::CreateHandle(
  (max_dead_count > kMaxCountForPackedCounts)) {
  constexpr int B = sizeof(std::atomic<LargeCounts>);
  // Round byte offset to proper alignment
  - static_assert(sizeof(std::atomic<LargeCounts>) >=
  - alignof(std::atomic<LargeCounts>));
  + static_assert(
  + sizeof(std::atomic<LargeCounts>) >= alignof(std::atomic<LargeCounts>),
  + "std::atomic<LargeCounts> must be packed");
  int64 offset = ((static_cast<int64>(next_offset_) + B - 1) / B) * B;
  result.byte_offset_ = offset;
  result.is_large_ = true;
  @@ -378,7 +379,8 @@ inline PendingCounts::Handle PendingCounts::Layout::CreateHandle(
  } else {
  result.byte_offset_ = next_offset_;
  result.is_large_ = false;
  - static_assert(sizeof(std::atomic<PackedCounts>) == 1);
  + static_assert(sizeof(std::atomic<PackedCounts>) == 1,
  + "std::atomic<PackedCounts> should be a single byte");
  next_offset_ += sizeof(std::atomic<PackedCounts>);
  }
  return result;
  