[Serializer] serialize the parent module of NormalProtocolConformance.

We used to just use FileContext at deserialization time. That causes
multiple NormalProtocolConformances with the same protocol and type,
but from different modules. And we will have issues at IRGen.

With this commit, we serialize the parent module and deserialize the parent
module, and we are not going to have multiple NormalProtocolConformances with
the same protocol and type.

rdar://16809311


Swift SVN r17675

include/swift/Serialization/ModuleFormat.h

@@ -902,6 +902,7 @@ namespace decls_block {
   using NormalProtocolConformanceLayout = BCRecordLayout<
     NORMAL_PROTOCOL_CONFORMANCE,
     DeclIDField, // the protocol
+    ModuleIDField,
     BCVBR<5>, // value mapping count
     BCVBR<5>, // type mapping count
     BCVBR<5>, // inherited conformances count