gpu/khronos_glcts_support: add support for GN builds

gpu/khronos_glcts_support/khronos_glcts_cts.gyp

 # Copyright 2014 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.
 
 {
   'includes': [
     'khronos_glcts.gypi',
+    'khronos_glcts_defaults.gypi',
   ],
   'targets': [
     {
       'target_name': 'glcts_common',
       'type': 'static_library',
       'conditions': [
         ['OS=="linux"', {
           'cflags_cc': [
             # WA: Suppress "implicit conversion turns string literal into
             # bool" compile warning from glcShaderIndexingTests.cpp,
@@ skipping 77 matching lines @@
       },
       'export_dependent_settings': [
         'glcts_common',
       ],
       'sources': [
         '<@(glcts_es2_srcs)',
       ],
     },
   ],
 }