Another patch wants to remove these files and we found that on (non-cygwin) Windows, they're being held by the non-find based status file searching. We didn't notice before since nothing else worked on these files after that.
Created attachment 443616 [details]
This is a file descriptor leak anyway, great that you caught it.
Committed r285522 (244039@main): <https://commits.webkit.org/244039@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 443616 [details].