Never use the hermetic xcode toolchain for iOS recipes.

scripts/slave/recipes/ios/try.expected/swarming_tests_skipped.json

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "name": "host and tools info",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />OS X 1.2.3, Xcode 6.7.8 (5D342509a)@@@",
@@ skipping 253 matching lines @@
       "python",
       "-u",
       "[BUILDER_CACHE]/ios_simulator_swarming/src/build/gyp_chromium",
       "--analyzer",
       "{\"additional_compile_targets\": [\"All\", \"fake test\"], \"files\": [\"foo.cc\"], \"test_targets\": [\"fake test\"]}",
       "/path/to/tmp/json"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "GYP_CROSSCOMPILE": "1",
-      "GYP_DEFINES": "OS=ios component=static_library fake gyp define 1='fake value 1' fake gyp define 2='fake value 2'"
+      "GYP_DEFINES": "OS=ios component=static_library fake gyp define 1='fake value 1' fake gyp define 2='fake value 2' target_arch=x64"
     },
     "name": "analyze",
     "~followup_annotations": [
       "@@@STEP_TEXT@No compile necessary@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"compile_targets\": [], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"status\": \"No dependency\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"test_targets\": []@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
@@ skipping 193 matching lines @@
   {
     "cmd": [],
     "name": "trigger"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]