/usr/include/libhashkit/ is in libhashkit-dev 1.0.18-4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libhashkit-1.0/algorithm.h
/usr/include/libhashkit-1.0/behavior.h
/usr/include/libhashkit-1.0/configure.h
/usr/include/libhashkit-1.0/digest.h
/usr/include/libhashkit-1.0/function.h
/usr/include/libhashkit-1.0/has.h
/usr/include/libhashkit-1.0/hashkit.h
/usr/include/libhashkit-1.0/hashkit.hpp
/usr/include/libhashkit-1.0/str_algorithm.h
/usr/include/libhashkit-1.0/strerror.h
/usr/include/libhashkit-1.0/string.h
/usr/include/libhashkit-1.0/types.h
/usr/include/libhashkit-1.0/visibility.h
/usr/include/libhashkit/hashkit.h