In support of long-running programs in which the users would like to be able
to jump to the source of a definition of any of the dependencies (itself
included) of the program.
* guix/build/asdf-build-system.scm (library-outputs): Move from here ...
* guix/build/lisp-utils.scm (library-outputs): ... to here.
(build-program): Accept dependency-prefixes argument, to allow the caller to
specify references which should be retained. Default to the library's output.
(build-image): Likewise.
(generate-executable): Likewise.
* gnu/packages/lisp.scm (sbcl-stumpwm+slynk, sbcl-slynk, sbcl-stumpwm): Adjust
accordingly to the new interface.
(sbcl-stumpwm+slynk)[native-inputs]: Move to ...
[inputs]: ... here.