fixup! bootstrap: move embedded snapshot to SnapshotBuilder

Co-authored-by: Anna Henningsen <github@addaleax.net>

Author: joyeecheung

src/node_snapshotable.cc

@@ -92,14 +92,8 @@ const SnapshotData* SnapshotBuilder::GetEmbeddedSnapshotData() {
   return ss.str();
 }
 
-std::unique_ptr<ExternalReferenceRegistry> SnapshotBuilder::registry_ = nullptr;
-Mutex SnapshotBuilder::snapshot_data_mutex_;
-
 const std::vector<intptr_t>& SnapshotBuilder::CollectExternalReferences() {
-  Mutex::ScopedLock lock(snapshot_data_mutex_);
-  if (registry_ == nullptr) {
-    registry_.reset(new ExternalReferenceRegistry());
-  }
+  static auto registry = std::make_unique<ExternalReferenceRegistry>();
   return registry_->external_references();
 }