add Build-Mac-Clang-arm64-Debug-iOS to CQ

This doesn't really add any CQ load.  We're already running
Test-iOS-Clang-iPhone7-GPU-GT7600-arm64-Debug-All which depends on this.
It'll just help make iOS Build failures stand out from Test failures.

Change-Id: I8614dd32d0ff3797357bfa41ea46d2571ec7976d
Reviewed-on: https://skia-review.googlesource.com/145725
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
1 file changed