/usr/bin/clang-tidy-3.5 is in clang-3.5 1:3.5.2-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/llvm-3.5/bin/clang-tidy
/usr/bin/../lib/llvm-3.5/bin/clang-tidy