swift234

Runtime: Reserve some protocol descriptor bits to identify special protocols.

We need to be able to easily recognize ErrorType in the runtime (and AnyObject, which we recognize by strcmp'ing in a few places currently, which is terrible). Carve out a byte in the protocol descriptor and existential type metadata flags where we can store an enumerator to identify interesting protocols and their existential types. While we're here, move the ProtocolDescriptorFlags and ExistentialTypeFlags up to swift/ABI/MetadataValues.h so their layout can be shared easily from IRGen and the runtime. NFC yet (except you're now arbitrarily limited to 16M protocols in a composition instead of 2G, but hopefully nobody will notice).

Swift SVN r26361