gnu: Move pkg-config to native inputs.

* gnu/packages/xiph.scm (ao)[native-inputs]: Move pkg-config from
inputs.
* gnu/packages/xorg.scm (xf86-video-geode)[native-inputs]: Likewise.

gnu/packages/xiph.scm

@@ -166,9 +166,11 @@ stereo encoding, and voice activity detection.")
     ;; XXX: Should back-ends be pushed to different outputs?  For instance,
     ;; "out" would include only the ALSA back-end, while "pulse" would
     ;; contain 'lib/ao/plugins-4/libpulse.*'.
-    (inputs `(("pkg-config" ,pkg-config)
-              ("alsa-lib" ,alsa-lib)
-              ("pulseaudio" ,pulseaudio)))
+    (inputs
+     `(("alsa-lib" ,alsa-lib)
+       ("pulseaudio" ,pulseaudio)))
+    (native-inputs
+     `(("pkg-config" ,pkg-config)))
     (synopsis "Cross platform audio library")
     (description
      "Libao is a cross-platform audio library that allows programs to

gnu/packages/xorg.scm

@@ -2710,8 +2710,8 @@ framebuffer device.")
            "19y13xl7yfrgyis92rmxi0ld95ajgr5il0n9j1dridwzw9aizz1q"))
         (patches (list (search-patch "xf86-video-geode-glibc-2.20.patch")))))
     (build-system gnu-build-system)
-    (inputs `(("pkg-config" ,pkg-config)
-              ("xorg-server" ,xorg-server)))
+    (inputs `(("xorg-server" ,xorg-server)))
+    (native-inputs `(("pkg-config" ,pkg-config)))
     (supported-systems
      ;; This driver is only supported on i686 systems.
      (filter (lambda (system) (string-prefix? "i686-" system))