gnu: gtk+ use modify-phases

* gnu/packages/gtk.scm (arguments): Replace alist-cons-before with modify-phases

gnu/packages/gtk.scm

@@ -673,9 +673,8 @@ application suites.")
       #:configure-flags (list (string-append "--with-html-dir="
                                              (assoc-ref %outputs "doc")
                                              "/share/gtk-doc/html"))
-      #:phases
-      (alist-cons-before
-       'configure 'pre-configure
+      #:phases (modify-phases %standard-phases
+        (add-before 'configure 'pre-configure
           (lambda _
             ;; Disable most tests, failing in the chroot with the message:
             ;; D-Bus library appears to be incorrectly set up; failed to read
@@ -685,8 +684,7 @@ application suites.")
             (substitute* "testsuite/Makefile.in"
               (("SUBDIRS = gdk gtk a11y css reftests")
                "SUBDIRS = gdk"))
-         #t)
-       %standard-phases)))
+            #t)))))
    (native-search-paths
     (list (search-path-specification
            (variable "GUIX_GTK3_PATH")