This landed inadvertently as part of the macros deployment and the plan is either to run a review or back it out (or keep it under an experimental flag – unlikely in this case due to its nature).
I don't think it's at all true that it's "quite common" to land changes without a review. Some minor changes are considered bug fixes, and some changes land with underscores or flags to ensure they can develop in-tree (especially if they are more complex in terms of their integration with the compiler).
The exception here is C++ interoperability which is fairly different in nature and so is taking a path outlined in John's post here.