However, if they are enabled in the build, libobjc and libgfortran do build. Are they likely to be functional?
I'd hate to guess, seems make check would tell you if they do. I'd expect there might be an issue with selecting the right multilib variant in our branch. Other than that, I'd kind of hope they would just work. Though, things like default to next-runtime isn't going to work (I don't think) in -m64 land. -fgnu-runtime should cure that type of problem.
Let us know how it goes, I'm interested.