[ddc] Add --sound-null-safety flag and pass to CFE

https://dart-review.googlesource.com/c/sdk/+/149080 is required to
get errors if you try use weak .dill files when passing the
--sound-null-safety flag.

Added a new build target to copy the sound SDK outline .dill to
dart-sdk/lib/_internal. This is only part of dartdevc_test right
now. We will decide in the future if we are going to include this
in the released SDK or if we will have the build systems create
them as needed. For now in testing scenarios it appears to be part
of the SDK.

Change-Id: I3b31a894841f59b437658104e7ee9443ee67db93
Fixes: https://github.com/dart-lang/sdk/issues/41694
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/146962
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

https://dart.googlesource.com/sdk/+/72e559929f7c6db5f38a9b2ad52df67aec624dfc
1 file changed
tree: 90f8646a5e1eaaa0bb7aaa6e7239ec321c260331
  1. commits.json