This change compiles opt-out libraries with opt-out semantics even when
sound null safety was requested. The compile-time error that libraries
cannot opt out with sound null safety is still produces but spurious errors
from interpreting opt-out as opt-in are avoided.
This also aligns the compilation of from-source with from-dill for the
case of opt-out libraries in face of sound null safety.
Closes#43327
Change-Id: I19d659219b7c7b357d15fc5f1ca4415fe1fc4592
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166243
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Johnni Winther
749b622a6b