swift

d4ba753a - Downgrade the error about `#isolation` in `@_unsafeInheritExecutor` when the concurrency library is old

Downgrade the error about `#isolation` in `@_unsafeInheritExecutor` when the concurrency library is old The introduction of the error concerning use of `#isolation` within an `@_unsafeInheritExecutor` function was carefully staged between the concurrency library and compiler to avoid breaking source compatibility. However, it is a source compatibility break when dealing certain revisions of the concurrency library that adopted `#isolation` prior to the compiler error. Detect when the _Concurrency library doesn't have the necessary workarounds in it and downgrade the error to a warning. Fixes rdar://132023573.