gnu: coreutils: Move Perl to 'native-inputs'.

* gnu/packages/base.scm (coreutils): Add 'native-inputs' field.
  This should allow cross builds to have man pages, and work around this
  'dummy-man' bug:
  <http://git.yoctoproject.org/cgit.cgi/poky/plain/meta/recipes-core/coreutils/coreutils-8.22/fix-for-dummy-man-usage.patch>.

gnu/packages/base.scm

@@ -242,12 +242,11 @@ used to apply commands with arbitrarily long arguments.")
               "04hjzzv434fb8ak3hh3dyhdvg3hqjjwvjmjxqzk1gh2jh6cr8gjv"))))
    (build-system gnu-build-system)
    (inputs `(("acl"  ,acl)                        ; TODO: add SELinux
-             ("gmp"  ,gmp)
-
-             ;; Perl is needed to run tests; remove it from cross builds.
-             ,@(if (%current-target-system)
-                   '()
-                   `(("perl" ,perl)))))
+             ("gmp"  ,gmp)))
+   (native-inputs
+    ;; Perl is needed to run tests in native builds, and to run the bundled
+    ;; copy of help2man.
+    `(("perl" ,perl)))
    (outputs '("out" "debug"))
    (arguments
     `(#:parallel-build? #f            ; help2man may be called too early