gnu: gstreamer: Add search patch specification for 'GST_PLUGIN_SYSTEM_PATH'.

* gnu/packages/gstreamer.scm (gstreamer)[native-search-paths]: New field.

gnu/packages/gstreamer.scm

@@ -171,6 +171,10 @@ (define-public gst-plugins-base
           ;; for g-ir-scanner.
           (setenv "CC" "gcc"))
         %standard-phases)))
+    (native-search-paths
+     (list (search-path-specification
+            (variable "GST_PLUGIN_SYSTEM_PATH")
+            (files '("lib/gstreamer-1.0")))))
     (home-page "http://gstreamer.freedesktop.org/")
     (synopsis
      "Plugins for the GStreamer multimedia library")