message: Add missing core-export
diff: #pragma once
  +#include "caf/detail/core_export.hpp"
  #include "caf/error.hpp"
  #include "caf/serializer.hpp"
  namespace caf::detail {
  -class serialized_size_inspector final : public serializer {
  +class CAF_CORE_EXPORT serialized_size_inspector final : public serializer {
  public:
  using super = serializer;
  