[Serialization] Preserve private discriminators through serialization.

Part of rdar://problem/17632175

Swift SVN r21611

include/swift/Serialization/DeclTypeRecordNodes.def

@@ -160,6 +160,8 @@ TRAILING_INFO(GENERIC_PARAM)
 TRAILING_INFO(GENERIC_REQUIREMENT)
 TRAILING_INFO(LAST_GENERIC_REQUIREMENT)
 
+OTHER(DISCRIMINATOR, 249)
+
 OTHER(NO_CONFORMANCE, 250)
 OTHER(NORMAL_PROTOCOL_CONFORMANCE, 251)
 OTHER(SPECIALIZED_PROTOCOL_CONFORMANCE, 252)

include/swift/Serialization/ModuleFile.h

@@ -250,6 +250,8 @@ private:
   std::unique_ptr<SerializedDeclTable> ClassMembersByName;
   std::unique_ptr<SerializedDeclTable> OperatorMethodDecls;
 
+  llvm::DenseMap<const ValueDecl *, Identifier> PrivateDiscriminatorsByValue;
+
   TinyPtrVector<Decl *> ImportDecls;
 
   using DeclIDVector = SmallVector<serialization::DeclID, 4>;

include/swift/Serialization/ModuleFormat.h

@@ -40,7 +40,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// Serialized module format minor version number.
 ///
 /// When the format changes IN ANY WAY, this number should be incremented.
-const uint16_t VERSION_MINOR = 131;
+const uint16_t VERSION_MINOR = 132;
 
 using DeclID = Fixnum<31>;
 using DeclIDField = BCFixed<31>;
@@ -947,6 +947,13 @@ namespace decls_block {
     BCFixed<1>                 // dummy
   >;
 
+  /// Specifies the discriminator string for a private declaration. This
+  /// identifies the declaration's original source file in some opaque way.
+  using DiscriminatorLayout = BCRecordLayout<
+    DISCRIMINATOR,
+    IdentifierIDField  // discriminator string, as an identifier
+  >;
+
   /// A placeholder for lack of conformance information. Conformances are
   /// indexed, so simply omitting one would be incorrect.
   using NoConformanceLayout = BCRecordLayout<