Fix LibWebRTC build for GStreamer versions older than 1.20

Author: philn

Source/WebCore/platform/graphics/gstreamer/GStreamerCommon.cpp

@@ -906,4 +906,13 @@ bool gstObjectHasProperty(GstPad* pad, const char* name)
 
 } // namespace WebCore
 
+#if !GST_CHECK_VERSION(1, 20, 0)
+GstBuffer* gst_buffer_new_memdup(gconstpointer data, gsize size)
+{
+    gpointer data2 = g_memdup2(data, size);
+
+    return gst_buffer_new_wrapped_full(static_cast<GstMemoryFlags>(0), data2, size, 0, size, data2, g_free);
+}
+#endif
+
 #endif // USE(GSTREAMER)

Source/WebCore/platform/graphics/gstreamer/GStreamerCommon.h

@@ -456,4 +456,8 @@ class GstIteratorAdaptor {
     bool m_started { false };
 };
 
+#if !GST_CHECK_VERSION(1, 20, 0)
+GstBuffer* gst_buffer_new_memdup(gconstpointer data, gsize size);
+#endif
+
 #endif // USE(GSTREAMER)