/usr/bin/clang-tidy-diff-4.0.py is in clang-tidy-4.0 1:4.0.1-10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/llvm-4.0/share/clang/clang-tidy-diff.py
/usr/bin/../lib/llvm-4.0/share/clang/clang-tidy-diff.py