Update build rules to point to Fuchsia SDK rather than Flutter's buildroot
Update build rules to point to Fuchsia SDK
rather than Flutter's buildroot

Change-Id: Ia6b3ac7fcec8d8276875b2adf8fc2cccc95b5dad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/117770
Reviewed-by: Chinmay Garde <2c5f961126c80cfe4f9b4f17931784885f34f766@google.com>
Reviewed-by: Zach Anderson <9f8b31e960a68dade71618f1ff6da6e23a1edfc9@google.com>
Commit-Queue: Zach Anderson <9f8b31e960a68dade71618f1ff6da6e23a1edfc9@google.com>

dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk