Also point gyp_angle back at tools.

BUG=angleproject:1569

Change-Id: Ib17ba6973db24aec9cd47000d869e5aa427c84a3
Reviewed-on: https://chromium-review.googlesource.com/727529Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>