gnu: tcsh: Use modify-phases.

* gnu/packages/shells.scm (tcsh)[arguments]: Use modify-phases.

gnu/packages/shells.scm

@@ -240,8 +240,8 @@ (define-public tcsh
      `(("ncurses" ,ncurses)))
     (arguments
      `(#:phases
-       (alist-cons-before
-        'check 'patch-test-scripts
+        (modify-phases %standard-phases
+          (add-before 'check 'patch-test-scripts
             (lambda _
               ;; Take care of pwd
               (substitute* '("tests/commands.at" "tests/variables.at")
@@ -257,15 +257,15 @@ (define-public tcsh
               ;; This file is ISO-8859-1 encoded.
               (with-fluids ((%default-port-encoding #f))
                 (substitute* "tests/testsuite"
-              (("/bin/sh") (which "sh")))))
-        (alist-cons-after
-         'install 'post-install
+                  (("/bin/sh") (which "sh"))))
+              #t))
+          (add-after 'install 'post-install
             (lambda* (#:key inputs outputs #:allow-other-keys)
               (let* ((out (assoc-ref %outputs "out"))
                      (bin (string-append out "/bin")))
                 (with-directory-excursion bin
-             (symlink "tcsh" "csh"))))
-         %standard-phases))))
+                  (symlink "tcsh" "csh"))
+                #t))))))
     (home-page "http://www.tcsh.org/")
     (synopsis "Unix shell based on csh")
     (description