Use bundled SDK 10.12 toolchain for Mac and iOS.

BUG=webrtc:6608, webrtc:8099, chromium:659726, chromium:763440
TBR=mbonadei@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2995033002
Cr-Commit-Position: refs/heads/master@{#19753}
diff --git a/DEPS b/DEPS
index 1db7232..b9f0cb5 100644
--- a/DEPS
+++ b/DEPS
@@ -177,6 +177,12 @@
     'pattern': '.',
     'action': ['python', 'src/build/vs_toolchain.py', 'update'],
   },
+  {
+    # Update the Mac toolchain if necessary.
+    'name': 'mac_toolchain',
+    'pattern': '.',
+    'action': ['python', 'src/build/mac_toolchain.py'],
+  },
   # Pull binutils for linux, enabled debug fission for faster linking /
   # debugging when used with clang on Ubuntu Precise.
   # https://code.google.com/p/chromium/issues/detail?id=352046