Notably, this carries us across the gcc->llvm transition.
Change-Id: I46203749c64c7ef0f52de40abcd4a073517cb06f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330949
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Zach Anderson <zra@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>