This is caused, through several layers of absurdity, by runtime type
information of Nix things being invisible due to -fvisibility=hidden
inside n-e-j.
We don't have any idea why n-e-j has -fvisibility=hidden, since blame
says it's from the initial commit. It is plausible that it was some
ill-advised optimization but it's not sound.
The crash is caused by dynamic_cast<RootArgs *>(MyArgs *) failing, which
is in turn caused by the RTTI being invisible.
See: https://www.qt.io/blog/quality-assurance/one-way-dynamic_cast-across-library-boundaries-can-fail-and-how-to-fix-it
Fixes: #2
