gnu: qpdf: Remove run-time dependency on Perl.

* gnu/packages/pdf.scm (qpdf)[source](snippet): New field.
[arguments]: Add #:disallowed-references.
[inputs]: Move PERL to...
[native-inputs]: ... here.

gnu/packages/pdf.scm

@@ -471,10 +471,21 @@ (define-public qpdf
             (uri (string-append "mirror://sourceforge/qpdf/qpdf-"
                                 version ".tar.gz"))
             (sha256 (base32
-                     "1lq1v7xghvl6p4hgrwbps3a13ad6lh4ib3myimb83hxgsgd4n5nm"))))
+                     "1lq1v7xghvl6p4hgrwbps3a13ad6lh4ib3myimb83hxgsgd4n5nm"))
+            (modules '((guix build utils)))
+            (snippet
+             ;; Replace shebang with the bi-lingual shell/Perl trick to remove
+             ;; dependency on Perl.
+             '(substitute* "qpdf/fix-qdf"
+                (("#!/usr/bin/env perl")
+                 "\
+eval '(exit $?0)' && eval 'exec perl -wS \"$0\" ${1+\"$@\"}'
+  & eval 'exec perl -wS \"$0\" $argv:q'
+    if 0;\n")))))
    (build-system gnu-build-system)
    (arguments
-      '(#:phases (alist-cons-before
+    `(#:disallowed-references (,perl)
+      #:phases (alist-cons-before
                 'configure 'patch-paths
                 (lambda _
                   (substitute* "make/libtool.mk"
@@ -486,12 +497,12 @@ (define-public qpdf
                     (("/usr/bin/env") (which "env"))))
                 %standard-phases)))
    (native-inputs
-    `(("pkg-config" ,pkg-config)))
+    `(("pkg-config" ,pkg-config)
+      ("perl" ,perl)))
    (propagated-inputs
     `(("pcre" ,pcre)))
    (inputs
-    `(("zlib" ,zlib)
-      ("perl" ,perl)))
+    `(("zlib" ,zlib)))
    (synopsis "Command-line tools and library for transforming PDF files")
    (description
     "QPDF is a command-line program that does structural, content-preserving