Implement dependent layouts for raw types

Update raw_layout.swift

Allow for concrete specializations of raw layout

Make test platform agnostic

lib/IRGen/GenTuple.cpp

@@ -512,7 +512,7 @@ namespace {
     }
 
     StructLayout performLayout(ArrayRef<const TypeInfo *> fieldTypes) {
-      return StructLayout(IGM, /*decl=*/nullptr, LayoutKind::NonHeapObject,
+      return StructLayout(IGM, /*type=*/ llvm::None, LayoutKind::NonHeapObject,
                           LayoutStrategy::Universal, fieldTypes);
     }
   };