I was reading some GCC bug reports and I found a more correct way to build libgcc:
$ mkdir build
$ cd build
$ ../configure --prefix /home/eric/dev/tios/toolchain --target=tms9900 --enable-languages=c
$ make all-gcc all-target-libgcc
$ make install
This is way easier and a lot more convenient than the directions I had before. I think that as long as I'm doing libraries, I'll try libiberty and see what happens.