That would fix the -threaded/unthreaded disparity. But I still don't
see how to access this stuff properly from foreign-primops in a library
such that GHCI doesn't barf when trying to load the library....

If you're referring to the problem with the missing stg_MUT_VAR_CLEAN_info symbol, I'll push a fix for that soon. Or is there something else?

Ah, yes, I think that will be addressed by your fix. It's good to hear that it is considered an ok thing to depend on RTS symbols under all "ways".