gnu: xvid: Use 'modify-phases'.

* gnu/packages/video.scm (xvid)[arguments]: Use 'modify-phases'.

gnu/packages/video.scm

@@ -1170,13 +1170,13 @@ format changes.")
     (native-inputs `(("yasm" ,yasm)))
     (arguments
      '(#:phases
-       (alist-cons-before
+       (modify-phases %standard-phases
+         (add-before
           'configure 'pre-configure
           (lambda _
             (chdir "build/generic")
             (substitute* "configure"
-            (("#! /bin/sh") (string-append "#!" (which "sh")))))
-        %standard-phases)
+              (("#! /bin/sh") (string-append "#!" (which "sh")))))))
        ;; No 'check' target.
        #:tests? #f))
     (home-page "https://www.xvid.com/")