Could you try the attached patches and see if things work for you with
a command such as:

--8<---------------cut here---------------start------------->8---
guix shell -C sbcl sbcl-gsll gcc-toolchain -- ...
--8<---------------cut here---------------end--------------->8---

There may be a way to patch our CFFI package to fix the links to all the
GCC toolchain things, which would allow us to remove gcc-toolchain in
the command above, but it will probably not be super easy.