[torque] fix memory leak

Change-Id: I9ca9d0d81ed37bdddd3286b3ebc46f2ecdacb248
Reviewed-on: https://chromium-review.googlesource.com/1063612Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53228}

src/torque/declarations.cc

@@ -232,7 +232,8 @@ Macro* Declarations::DeclareMacro(const std::string& name,
       ReportError(s.str());
     }
   }
-  return macro_list->AddMacro(new Macro(name, signature));
+  return macro_list->AddMacro(
+      RegisterDeclarable(std::unique_ptr<Macro>(new Macro(name, signature))));
 }
 
 Builtin* Declarations::DeclareBuiltin(const std::string& name,