So again thanks to Sverx, I think I have the DS build of Anguna working again.
In response to one of my previous posts lamenting that I couldn't find a 2008 release of the devkitPro/libnds tools, he mentioned that he had a copy! He sent me what he had, which turned out to be the windows version.
Although GBA anguna was developed on windows, I developed the DS version on linux. So everything I had was set up for linux, and I'm currently using (and running my builds on) linux.
My first attempt to get it working was to just use my current version of my gcc arm cross-compiler with the 2008 version of libnds, which as I suspected didn't work. It compiled, but the linker complained about all sorts of things.
I didn't want to go all the way and set up everything in windows yet, so the next try was stupid: use all the windows toolchain compilers via wine. Has anyone EVER run windows versions of gcc on linux using wine before? A terrible idea. But it seemed to work when I compiled it. (despite taking quite a while to compile!) But when I ran the finished rom, it had all sorts of weird issues once you got into the game, past the splash screens.
But this seemed familiar, similar to the problems I had trying to compile the gba version on linux recently. So I went through and made sure to convert all the files' line endings to unix (not sure why that would be an issue, since they were originally done in linux), but then everything worked!
So despite the terrible idea of running all compilers in wine, I know have DS builds working again. (I think? I haven't tested it yet past the first couple of rooms)
Maybe that means the new dungeon will eventually get ported to the DS!