/usr/share/doc/clang-6.0/changelog.Debian.gz is in clang-6.0 1:6.0-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/clang-6.0/../libllvm6.0/changelog.Debian.gz
/usr/share/doc/clang-6.0/../libllvm6.0/changelog.Debian.gz