packages: Disambiguate 'modules' and 'imported-modules' in <origin>.

The two mistakes made here (confusion between 'modules' and
'imported-modules') were canceling each other.

* guix/packages.scm (patch-and-repack): Use IMPORTED-MODULES, not
MODULES, as the base of the module list passed as #:modules to
'gexp->derivation'.
(origin->derivation): Pass IMPORTED-MODULES, not MODULES, as
the #:imported-modules argument of 'patch-and-repack'.
* gnu/packages/engineering.scm (fastcap)[source]: Add 'imported-modules'
field.

gnu/packages/engineering.scm

@@ -232,6 +232,7 @@ optimizer; and it can produce photorealistic and design review images.")
               (modules '((guix build utils)
                          (guix build download)
                          (guix ftp-client)))
+              (imported-modules modules)
               (patches (search-patches "fastcap-mulSetup.patch"
                                        "fastcap-mulGlobal.patch"))))
     (build-system gnu-build-system)

guix/packages.scm

@@ -544,7 +544,8 @@ IMPORTED-MODULES specify modules to use/import for use by SNIPPET."
                                           "--files-from=.file_list")))))))))
 
     (let ((name    (tarxz-name original-file-name))
-          (modules (delete-duplicates (cons '(guix build utils) modules))))
+          (modules (delete-duplicates (cons '(guix build utils)
+                                            imported-modules))))
       (gexp->derivation name build
                         #:graft? #f
                         #:system system
@@ -1152,7 +1153,7 @@ cross-compilation target triplet."
                          #:flags flags
                          #:system system
                          #:modules modules
-                         #:imported-modules modules
+                         #:imported-modules imported-modules
                          #:guile-for-build guile)))))
 
 (define-gexp-compiler (origin-compiler (origin origin?) system target)