It me took quite a lot of reading and thinking and trial and error to get Bash to install itself where I thought it should go. The configuration options I used are
./configure --prefix=/mnt/target/usr/local --exec-prefix=/mnt/target --with-curses
Once you have made and installed Bash, you need to make a symlink like this
cd /mnt/target/bin; ln -s bash sh. This is because scripts usually
have a first line like this
#!/bin/sh
If you don't have the symlink, your scripts won't be able to run, because
they will be looking for /bin/sh not /bin/bash.
You could reboot again at this point if you like. You should notice that
the scripts actually run this time, though you still can't login, because
there are no getty or login programs.