This came up in bug 938569. net-libs/libktorrent uses <xfs/xfs.h> if available at https://invent.kde.org/network/libktorrent/-/blob/master/src/util/fileops.cpp#L302. (Not checked if it's a header-only dep.)
Appears to be header-only… $ scanelf -n /usr/lib64/libKTorrent6.so TYPE NEEDED FILE ET_DYN libKF6Archive.so.6,libgcrypt.so.20,libgmp.so.10,libQt6Core5Compat.so.6,libKF6KIOCore.so.6,libQt6Network.so.6,libKF6I18n.so.6,libQt6Xml.so.6,libKF6CoreAddons.so.6,libKF6ConfigCore.so.6,libQt6Core.so.6,libstdc++.so.6,libgcc_s.so.1,libc.so.6 /usr/lib64/libKTorrent6.so
This needs a new CMake option in (ideally upstream's) CMakelists.txt.