[deserialization] Begin move to lazy linking by putting a SerializedModuleLoader on SILModule.

Right now it is not wired up. That is coming in forthcoming commits. I am trying
to be very incremental about this.

This series of patches will fix an assertion triggered by us not deserializing
functions from vtables appropriately. Doing linking lazily fixes that issue and
does the "right thing".

The work is being done in consultation with John, Joe, and Jordan.

Swift SVN r14479

lib/SIL/SILModule.cpp

@@ -12,6 +12,7 @@
 
 #include "swift/SIL/SILModule.h"
 #include "swift/SIL/SILExternalSource.h"
+#include "swift/Serialization/SerializedSILLoader.h"
 #include "swift/SIL/SILValue.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -41,9 +42,45 @@ void SILExternalSource::anchor() {
 /// SILModule that these things are uniqued into.
 typedef llvm::FoldingSet<SILTypeList> SILTypeListUniquingType;
 
+class SILModule::SerializationCallback : public SerializedSILLoader::Callback {
+  void didDeserialize(Module *M, SILFunction *fn) override {
+    updateLinkage(fn);
+  }
+
+  void didDeserialize(Module *M, SILGlobalVariable *var) override {
+    updateLinkage(var);
+  }
+
+  void didDeserialize(Module *M, SILVTable *vtable) override {
+    // TODO: should vtables get linkage?
+    //updateLinkage(vtable);
+  }
+
+  template <class T> void updateLinkage(T *decl) {
+    switch (decl->getLinkage()) {
+    case SILLinkage::Public:
+      decl->setLinkage(SILLinkage::PublicExternal);
+      return;
+    case SILLinkage::Hidden:
+      decl->setLinkage(SILLinkage::HiddenExternal);
+      return;
+    case SILLinkage::Shared:
+      decl->setLinkage(SILLinkage::Shared);
+    case SILLinkage::Private: // ?
+    case SILLinkage::PublicExternal:
+    case SILLinkage::HiddenExternal:
+      return;
+    }
+  }
+};
+
 SILModule::SILModule(Module *SwiftModule)
-  : TheSwiftModule(SwiftModule), Stage(SILStage::Raw), Types(*this) {
+  : TheSwiftModule(SwiftModule), Stage(SILStage::Raw),
+    Callback(new SILModule::SerializationCallback()), Types(*this) {
   TypeListUniquing = new SILTypeListUniquingType();
+  SILLoader = SerializedSILLoader::create(getASTContext(), this,
+                                          Callback.get());
+
 }
 
 SILModule::~SILModule() {