Fix rm.exe "Permission denied" errors on Windows
I haven't built a universal exe on Windows for a while. Doing it today produced "Permission denied" errors afterward when running "make clean". Claude fixed it and produced the following comment:
"On Windows, `ln -s` to a directory creates a native directory symlink that MSYS
rm cannot unlink, so `rm -rf temp_builds` fails with `Permission denied` and
`make clean` breaks after a universal build.
Fix: in universalclean, run `find ... -type l -exec rmdir {} +` first, which
unlinks such a link without following it. On Linux/macOS rmdir refuses POSIX
symlinks; `|| true` absorbs the error and `rm -rf` behaves exactly as before."
closes https://github.com/official-stockfish/Stockfish/pull/7038
No functional change