[Serialization] Make requirement signature conformance loading lazy.

The previous commit needed this for the importer, so we might as well
take advantage of it in deserialization as well. No expected change in
behavior.

Author: jrose-apple

lib/Serialization/Deserialization.cpp

@@ -654,16 +654,6 @@ NormalProtocolConformance *ModuleFile::readNormalConformance(
   dc->getAsNominalTypeOrNominalTypeExtensionContext()
     ->registerProtocolConformance(conformance);
 
-  // Read requirement signature conformances.
-  SmallVector<ProtocolConformanceRef, 4> reqConformances;
-  for (const auto &req : proto->getRequirementSignature()) {
-    if (req.getKind() == RequirementKind::Conformance) {
-      auto reqConformance = readConformance(DeclTypeCursor);
-      reqConformances.push_back(reqConformance);
-    }
-  }
-  conformance->setSignatureConformances(reqConformances);
-
   // If the conformance is complete, we're done.
   if (conformance->isComplete())
     return conformance;
@@ -4594,13 +4584,16 @@ void ModuleFile::finishNormalConformance(NormalProtocolConformance *conformance,
                                               typeCount,
                                               rawIDs);
 
-  // Skip requirement signature conformances.
-  auto proto = conformance->getProtocol();
+  // Read requirement signature conformances.
+  const ProtocolDecl *proto = conformance->getProtocol();
+  SmallVector<ProtocolConformanceRef, 4> reqConformances;
   for (const auto &req : proto->getRequirementSignature()) {
     if (req.getKind() == RequirementKind::Conformance) {
-      (void)readConformance(DeclTypeCursor);
+      auto reqConformance = readConformance(DeclTypeCursor);
+      reqConformances.push_back(reqConformance);
     }
   }
+  conformance->setSignatureConformances(reqConformances);
 
   ArrayRef<uint64_t>::iterator rawIDIter = rawIDs.begin();