hello. I recently ran into this problem. To get around it, I built devel/libffi by hand, , installed it, then rebuilt all the packages that depend on libffi, incluting gobject-introspection. In order for me to do this, I needed to pkg_delete the existing version of gobject-introspection on the build system in order to get things to build. Once I did that, however, the process of moving to libffi version 8 was pretty straightforward. This is with pkgsrc sources as of January 24, 2022.
-thanks -Brian
