[dart] Add support for the arm64c architecture

Change-Id: I2d1d81b58c6de9043123f2812b4f0586df4d1be1
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/188520
Auto-Submit: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: William Hesse <whesse@google.com>
2 files changed