message: span: remove rbegin(), rend() because they're broken
  See std::reverse_iterator if this actually needed (note that
  forward_iterator_tag is also wrong in that case).
  I don't see a reason why those are defined in a macro, either.
diff: #define ADIOS2_iterators_functions(DATA_FUNCTION, SIZE_FUNCTION) \
  iterator begin() noexcept { return iterator(DATA_FUNCTION); } \
  - iterator end() noexcept \
  - { \
  - return iterator(DATA_FUNCTION + SIZE_FUNCTION); \
  - } \
  - iterator rbegin() noexcept { return --end(); } \
  - iterator rend() noexcept { return --begin(); }
  + iterator end() noexcept { return iterator(DATA_FUNCTION + SIZE_FUNCTION); }
  #endif /* ADIOS2_ADIOSMACROS_H */
  