swift234

Summon the eldritch horror "EagerDeserializationDecls" from the bowels of history.

Adding explicit constructors to Clang-imported structs in the previous commits exposes a latent phase ordering issue between the Clang importer and SIL deserialization. Deserializing the standard library SIL ends up pulling in additional Clang decls which never get type-checked before we attempt to emit their code. Work around this by bringing back the "EagerDeserializedDecls" block in the serialization format, and adding any cross-referenced decls that get referenced in SILSerializeAll mode to it, so that we ensure they're available before SILGen. We also have to type-check external decls after doing so, since when only importing a module, we wouldn't do any type-checking at all otherwise.

Swift SVN r23728