This generalizes the mechanism by which the Emacs dependencies are made visible,
so that any build phase can make use of them.
* guix/build/emacs-build-system.scm (%legacy-install-suffix): New variable.
(%install-suffix): Redefine in terms of %legacy-install-suffix.
(set-emacs-load-path): Add new phase used for dependency resolution.
(build): Remove ad-hoc dependency discovery mechanism.
(emacs-input->el-directory): Add new procedure.
(emacs-inputs-el-directories): Use it.
(package-name-version->elpa-name-version): Fix typo.
(%standard-phases): Include the new `set-emacs-load-path' phase. Refactor to
make the ordering of the phases clearer.
* guix/build/emacs-utils.scm (emacs-byte-compile-directory): Remove the
optional `dependency-dirs' argument, which is now obsoleted by the
`set-emacs-load-path' phase.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>