Fixes <https://bugs.gnu.org/36925>.
Reported by Jesse Gibbons <jgibbons2357@gmail.com>.
* guix/scripts/pack.scm (wrapped-package): Add 'output*' parameter.
[build]: Define 'input' and 'target'; use them instead of #$package and
#$output, respectively.
(wrapped-manifest-entry): New procedure.
(map-manifest-entries): Call PROC directly.
(guix-pack): Pass WRAPPED-MANIFEST-ENTRY to 'map-manifest-entries'.