gnu: mesa: Use 'modify-phases'.

* gnu/packages/gl.scm (mesa)[arguments]: Use 'modify-phases' syntax.

gnu/packages/gl.scm

@@ -252,14 +252,16 @@ also known as DXTn or DXTC) for Mesa.")
               '())
              (_
               '("--with-dri-drivers=nouveau,r200,radeon,swrast"))))
-       #:phases (alist-cons-after
+       #:phases
+       (modify-phases %standard-phases
+         (add-after
            'unpack 'patch-create_test_cases
            (lambda _
              (substitute* "src/compiler/glsl/tests/lower_jumps/create_test_cases.py"
                (("/usr/bin/env bash") (which "bash")))
              (substitute* "src/intel/genxml/gen_pack_header.py"
-                     (("/usr/bin/env python2") (which "python"))))
-                 (alist-cons-before
+               (("/usr/bin/env python2") (which "python")))))
+         (add-before
            'build 'fix-dlopen-libnames
            (lambda* (#:key inputs outputs #:allow-other-keys)
              (let ((s2tc (assoc-ref inputs "s2tc"))
@@ -287,8 +289,7 @@ also known as DXTn or DXTC) for Mesa.")
                  ;; it's never installed since Mesa removed its
                  ;; egl_gallium support.
                  (("\"gbm_dri\\.so")
-                         (string-append "\"" out "/lib/dri/gbm_dri.so")))))
-                  %standard-phases))))
+                  (string-append "\"" out "/lib/dri/gbm_dri.so")))))))))
     (home-page "http://mesa3d.org/")
     (synopsis "OpenGL implementation")
     (description "Mesa is a free implementation of the OpenGL specification -