[dart] Support arm64c virtual architecture

Change-Id: I765f1982c48226ce1c18b952055c01cd4b4771e4
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/213940
Auto-Submit: Alexander Thomas <athom@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
15 files changed