Fields used in Dart test with `@Native` fields must be `extern "C"` to
avoid name mangling.
As seen from build and test failures, MSVC doesn't seem to consistently
use C fields for `extern "C"` fields defined in a C++ file.
By moving these fields into a C file, they can be referenced both from
the other C++ test functions and via Dart fields.
TEST=Windows CI build
Cq-Include-Trybots: luci.dart.try:vm-win-debug-x64-try,vm-win-debug-x64c-try,vm-aot-win-debug-x64c-try
Change-Id: Ia504a1d6e04efd00bdd50de54f4b65292ec7a41a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/342260
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Hossein Yousefi <yousefi@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Simon Binder
f2329a703f