swift

5a49e344 - Serialization: Error on xref to implementation-only dependencies

Serialization: Error on xref to implementation-only dependencies Introduce a last resort check reporting references to implementation-only dependencies that would appear in the generated swiftmodule. This check is applied at serialization, long after exportability checking applied at typechecking. It should act as a back stop to references missed by typechecking or @_implementationOnly decls that should have been skipped. This check is gated behind CheckImplementationOnlyStrict and should be used with embedded only. rdar://160697599