https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84075
--- Comment #9 from Christoph Hertzberg <chtz at informatik dot uni-bremen.de> --- Independent of this issue, the forward declaration in boost/serialization/shared_ptr_helper.hpp does not make sense. I created a PR to fix that: https://github.com/boostorg/serialization/pull/144
