gnu: webkitgtk-2.4, webkitgtk/gtk+-2, qt: Disable parallel builds.

* gnu/packages/webkit.scm (webkitgtk-2.4, webkitgtk/gtk+-2):
  Disable parallel builds as suggested in
  https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00837.html .
* gnu/packages/qt.scm (qt): Likewise.

gnu/packages/qt.scm

@@ -182,7 +182,12 @@ (define-public qt
        ("ruby" ,ruby)
        ("which" ,(@ (gnu packages base) which))))
     (arguments
-     `(#:phases
+     `(;; FIXME: Disabling parallel building is a quick hack to avoid the
+       ;; failure described in
+       ;; https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00837.html
+       ;; A more structural fix is needed.
+       #:parallel-build? #f
+       #:phases
          (alist-replace
           'configure
           (lambda* (#:key outputs #:allow-other-keys)

gnu/packages/webkit.scm

@@ -149,6 +149,11 @@ (define-public webkitgtk-2.4
     (build-system gnu-build-system)
     (arguments
      '(#:tests? #f ; no tests
+       ;; FIXME: Disabling parallel building is a quick hack to avoid the
+       ;; failure described in
+       ;; https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00837.html
+       ;; A more structural fix is needed.
+       #:parallel-build? #f
        #:phases (modify-phases %standard-phases
                   (add-after
                    'unpack 'set-gcc
@@ -163,7 +168,12 @@ (define-public webkitgtk/gtk+-2
   (package (inherit webkitgtk-2.4)
     (name "webkitgtk-gtk2")
     (arguments
-     `(#:configure-flags
+     `(;; FIXME: Disabling parallel building is a quick hack to avoid the
+       ;; failure described in
+       ;; https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00837.html
+       ;; A more structural fix is needed.
+       #:parallel-build? #f
+       #:configure-flags
        '("--enable-webkit2=no"
          "--with-gtk=2.0")
        ,@(package-arguments webkitgtk-2.4)))