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.