gnu: grep: Add missing dependency on Perl.

* gnu/packages/base.scm (grep)[native-inputs]: New field.
* gnu/packages/commencement.scm (grep-final): Likewise.

gnu/packages/base.scm

@@ -82,6 +82,7 @@ command-line arguments, multiple languages, and so on.")
              (base32
               "1srn321x7whlhs5ks36zlcrrmj4iahll8fxwsh1vbz3v04px54fa"))))
    (build-system gnu-build-system)
+   (native-inputs `(("perl" ,perl)))             ;some of the tests require it
    (synopsis "Print lines matching a pattern")
    (description
      "grep is a tool for finding text inside files.  Text is found by

gnu/packages/commencement.scm

@@ -728,7 +728,9 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
   ;; The final grep.  Gzip holds a reference to it (via zgrep), so it must be
   ;; built before gzip.
   (package-with-bootstrap-guile
-   (package-with-explicit-inputs grep
+   (package-with-explicit-inputs (package
+                                   (inherit grep)
+                                   (native-inputs `(("perl" ,perl-boot0))))
                                  %boot5-inputs
                                  (current-source-location)
                                  #:guile guile-final)))