gnu: python2-pygtk: fix path to pygobject-codegen-2.0

* gnu/packages/gtk.scm (python2-pygtk)[arguments]: Add phase to patch the path
  to the pygobject-codegen-2.0 executable.

gnu/packages/gtk.scm

@@ -752,6 +752,14 @@ extensive documentation, including API reference and a tutorial.")
     (arguments
      `(#:tests? #f
        #:phases (alist-cons-after
+                 'configure 'fix-codegen
+                 (lambda* (#:key inputs #:allow-other-keys)
+                   (substitute* "pygtk-codegen-2.0"
+                     (("^prefix=.*$")
+                      (string-append
+                       "prefix="
+                       (assoc-ref inputs "python-pygobject") "\n"))))
+                 (alist-cons-after
                   'install 'install-pth
                   (lambda* (#:key inputs outputs #:allow-other-keys)
                     ;; pygtk's modules are stored in a subdirectory of python's
@@ -765,7 +773,7 @@ extensive documentation, including API reference and a tutorial.")
                       (call-with-output-file (string-append site "/pygtk.pth")
                         (lambda (port)
                           (format port "gtk-2.0~%")))))
-                 %standard-phases)))
+                  %standard-phases))))
     (home-page "http://www.pygtk.org/")
     (synopsis "Python bindings for GTK+")
     (description