/usr/share/man/man3/wstrlen.3.gz is in libsynce0-dev 0.15-1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man3/wstr_to_ascii.3.gz
/usr/share/man/man3/wstr_to_ascii.3.gz