Update macOS FYI toolchain bot to compile with 10.12 SDK.

BUG=669240

Review-Url: https://codereview.chromium.org/2976533002
Cr-Commit-Position: refs/heads/master@{#485094}

tools/mb/mb_config.pyl

@@ -114,7 +114,7 @@
       'Chromium Linux32 Goma Canary (clobber)': 'release_bot_x86',
       'Chromium Mac 10.10 MacViews': 'mac_views_browser_release_bot',
       'Chromium Mac 10.11': 'release_bot',
-      'Chromium Mac 10.11 Force Mac Toolchain': 'release_bot_mac_hermetic',
+      'Chromium Mac 10.11 Force Mac Toolchain': 'release_bot_mac_new_sdk',
       'Chromium Mac 10.9 Goma Canary': 'release_bot',
       'Chromium Mac 10.9 Goma Canary (clobber)': 'release_bot',
       'Chromium Mac 10.9 Goma Canary (dbg)': 'debug_bot',
@@ -1433,8 +1433,8 @@
       'release_bot', 'chrome_with_codecs',
     ],
 
-    'release_bot_mac_hermetic': [
-      'release_bot', 'mac_hermetic_toolchain',
+    'release_bot_mac_new_sdk': [
+      'release_bot', 'mac_new_sdk',
     ],
 
     'release_bot_mac_strip': [
@@ -1776,8 +1776,8 @@
       'mixins': ['chrome_with_codecs'],
     },
 
-    'mac_hermetic_toolchain': {
-      'gn_args': 'use_system_xcode=false',
+    'mac_new_sdk': {
+      'gn_args': 'mac_sdk_min=10.12',
     },
 
     'headless': {