message: Fix build failure. build fails when type(std::string::length()) != uint64_t
diff: @@ -1600,7 +1600,7 @@ Translator::CreateMetadataVector() {
  // versions. Here we put a 16-byte dummy string as a placeholder. We choose
  // 16-byte because it's the alignment of buffers in flatbuffer, so it won't
  // cause any waste of space if the actual string is shorter than 16 bytes.
  - constexpr uint64_t kByteStringSize = 16;
  + constexpr std::size_t kByteStringSize = 16;
  metadata.push_back(
  BuildMetadata("min_runtime_version", std::string(kByteStringSize, '\0')));
  for (const auto& kv : metadata_) {
  