Turn the unresolved-references list into a linked list using the VariableProxies themselves

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index a5f83d50c9a9198ee329df3bd929ae0d879f0d73..56755f40afe523ef16d82f28091e464cb5443ba4 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -1665,6 +1665,8 @@ class VariableProxy final : public Expression {
 
   static int num_ids() { return parent_num_ids() + 1; }
   BailoutId BeforeId() const { return BailoutId(local_id(0)); }
+  void set_next_unresolved(VariableProxy* next) { next_unresolved_ = next; }
+  VariableProxy* next_unresolved() { return next_unresolved_; }
 
  protected:
   VariableProxy(Zone* zone, Variable* var, int start_position,
@@ -1693,6 +1695,7 @@ class VariableProxy final : public Expression {
     const AstRawString* raw_name_;  // if !is_resolved_
     Variable* var_;                 // if is_resolved_
   };
+  VariableProxy* next_unresolved_;
 };