message: Fix tracing_data_factory
diff: #pragma once
  +#include "caf/detail/core_export.hpp"
  #include "caf/fwd.hpp"
  namespace caf {
  /// Creates instances of @ref tracing_data.
  -class tracing_data_factory {
  +class CAF_CORE_EXPORT tracing_data_factory {
  public:
  virtual ~tracing_data_factory();
  