Linux: Add version script to restrict exported symbols (issue #1765)

libcef_dll/libcef.lst

@@ -0,0 +1,9 @@
+# Copyright 2016 The Chromium Embedded Framework Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+{
+  /* Only export necessary symbols from libcef.so. */
+  global: cef_*;
+  local: *;
+};