Make gyp target_arch setting native to chromium/config.py

scripts/slave/recipes/chromium_trybot.expected/linux_success_fail_net_unittests_debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_deps': {'src/third_party/WebKit/LayoutTests': None, 'src/webkit/data/layout_tests/LayoutTests': None}, 'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]"
     ],
@@ skipping 80 matching lines @@
     "name": "apply_issue"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1",
+      "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1 target_arch=x64",
       "GYP_GENERATORS": "ninja"
     },
     "name": "gclient runhooks"
   },
   {
     "abort_on_failure": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
@@ skipping 136 matching lines @@
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1",
+      "GYP_DEFINES": "component=shared_library dcheck_always_on=1 fastbuild=1 target_arch=x64",
       "GYP_GENERATORS": "ninja"
     },
     "name": "gclient runhooks (2)"
   },
   {
     "abort_on_failure": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
@@ skipping 84 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@for executable_name, ignored_failures in failures['ignored'].iteritems():@@@",
       "@@@STEP_LOG_LINE@python.inline@  if ignored_failures:@@@",
       "@@@STEP_LOG_LINE@python.inline@    print 'Ignored failures (%s):' % executable_name@@@",
       "@@@STEP_LOG_LINE@python.inline@    print '\\n'.join(sorted(ignored_failures))@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@sys.exit(0 if success else 1)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   }
 ]