bug#53002: guix can't find gfortran-toolchain or gdc-toolchain

[Jesse Gibbons]

Strange bug, guix can't find gfortran-toolchain even though it is a 
package defined publicly in one of the files it presumably searches.

`which guix` outputs the expected "$HOME/.config/guix/current/bin/guix", 
so it probably isn't a problem with my guix home.

`guix package -A gfortran` returns nothing.

`guix package -A gcc-toolchain` shows several different versions of 
gcc-toolchain in gnu/packages/commencement.scm

`guix edit gcc-toolchain` opens the source where guix presumably found 
the gcc-toolchain package definition. Within that file, 
gfortran-toolchain is defined publicly.

This is also the case for gdc-toolchain.

`guix describe`:

    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 8bfb1258d32b5ffeeefd9d44753b87f62bdbf822