raco exe: preserve `lib` form of runtime submodule references
raco exe: preserve `lib` form of runtime submodule references

Otherwise, executable creation can fail because a module is referenced
both through a `lib` path and through a filesystem path.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket