[deserialization] Add ClassDecl -> VTable map to SILModule.

Swift SVN r15545

lib/SIL/SILVTable.cpp

@@ -32,6 +32,7 @@ SILVTable *SILVTable::create(SILModule &M, ClassDecl *Class,
                          alignof(SILVTable));
   SILVTable *vt = ::new (buf) SILVTable(Class, Entries);
   M.vtables.push_back(vt);
+  M.VTableLookupTable[Class] = vt;
   return vt;
 }