[gn] Allow building a snapshot with unwinding information.

src/setup-isolate-deserialize.cc

Index: src/setup-isolate-deserialize.cc
diff --git a/src/setup-isolate-deserialize.cc b/src/setup-isolate-deserialize.cc
index a01bb5a3f8b1a9e33928e6701cd7aa75fab8f6f9..eec5f60a33f0496a755fc4dd37113f5149a9d6d2 100644
--- a/src/setup-isolate-deserialize.cc
+++ b/src/setup-isolate-deserialize.cc
@@ -20,6 +20,14 @@ void SetupIsolateDelegate::SetupBuiltins(Isolate* isolate,
 
 void SetupIsolateDelegate::SetupInterpreter(
     interpreter::Interpreter* interpreter, bool create_heap_objects) {
+#if defined(V8_USE_SNAPSHOT) && !defined(V8_USE_SNAPSHOT_WITH_UNWINDING_INFO)
+  if (FLAG_perf_prof_unwinding_info) {
+    OFStream os(stdout);
+    os << "Warning: The --perf-prof-unwinding-info flag can be passed at "
+          "mksnapshot time to get better results."
+       << std::endl;
+  }
+#endif
   DCHECK(interpreter->IsDispatchTableInitialized());
 }