There's a recipe in src/cmd/mkone (../mkone)?

I hope I haven't overlooked any of the mkfiles, it's been a bit of a
swamp for a while.

Have a look at each mkfile's first few lines, you can change ROOT
there or

	mk ROOT=$home/go

but I'm not always propagating (ever?) MKFLAGS.

Let me know, I'll be back in the (local) morning.  Off the cuff, I
don't think you're doing anything wrong, it looks like a context issue
I have not taken into consideration.  But I can't put my finger on it.

++L