Make Nexus5X bisect bot use 64 bit binaries.

scripts/slave/recipes/bisection/android_bisect.expected/basic_android_nexus5X_perf_bisect.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/android_nexus5X_perf_bisect",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 393 matching lines @@
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_CROSSCOMPILE": "1",
-      "GYP_DEFINES": "OS=android component=static_library fastbuild=1 gomadir='RECIPE_PACKAGE_REPO[build]/goma' target_arch=arm use_goma=1",
+      "GYP_DEFINES": "OS=android component=static_library fastbuild=1 gomadir='RECIPE_PACKAGE_REPO[build]/goma' target_arch=arm64 use_goma=1",
       "PATH": "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/build/android:%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [],
     "cwd": "[BUILDER_CACHE]/android_nexus5X_perf_bisect",
     "name": "***LEGACY BISECT (deprecated)***"
   },
   {
@@ skipping 193 matching lines @@
     "cwd": "[BUILDER_CACHE]/android_nexus5X_perf_bisect",
     "name": "gsutil upload",
     "~followup_annotations": [
       "@@@STEP_LINK@logcat dump@https://storage.cloud.google.com/chromium-android/logcat_dumps/android_nexus5X_perf_bisect/571@@@"
     ]
   },
   {
     "cmd": [
       "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/third_party/android_platform/development/scripts/stack",
       "--arch",
-      "arm",
+      "arm64",
       "--more-info",
       "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/out/Release/full_log"
     ],
     "cwd": "[BUILDER_CACHE]/android_nexus5X_perf_bisect",
     "env": {
       "CHROMIUM_OUTPUT_DIR": "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/out/Release",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "PATH": "[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/android_nexus5X_perf_bisect/src/build/android:%(PATH)s"
     },
     "name": "stack_tool_with_logcat_dump"
@@ skipping 43 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]