/usr/src/linux-headers-4.15.0-39-generic/arch/hexagon is in linux-headers-4.15.0-39-generic 4.15.0-39.42.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.15.0-39-generic/arch/../../linux-headers-4.15.0-39/arch/hexagon