Some linking fixes for GN build.

tools/xdisplaycheck/xdisplaycheck.gyp

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'targets': [
     {
+      # GN version: //tools/xdisplaycheck
       'target_name': 'xdisplaycheck',
       'type': 'executable',
       'dependencies': [
         '../../build/linux/system.gyp:x11',
       ],
       'sources': [
         'xdisplaycheck.cc',
       ],
     },
   ],
 }