Fix SDK build on Mac.

Change-Id: I42cb9ae19b6567d70af793c71ad93b8902cd37a0
Reviewed-on: https://dart-review.googlesource.com/c/86022
Commit-Queue: Samir Jindel <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>
Auto-Submit: Samir Jindel <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>

Author: sjindel-google

runtime/vm/v8_snapshot_writer.cc

@@ -75,7 +75,9 @@ void V8SnapshotProfileWriter::AttributeReferenceTo(ObjectId object_id,
 
   ASSERT(reference.offset_or_name >= 0);
   info->edges->Add({
-      reference.reference_type == Reference::kElement ? kElement : kProperty,
+      static_cast<intptr_t>(reference.reference_type == Reference::kElement
+                                ? kElement
+                                : kProperty),
       reference.offset_or_name,
       reference.to_object_id,
   });