/lib/modules/4.13.0-1018-azure/build is in linux-headers-4.13.0-1018-azure 4.13.0-1018.21.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.13.0-1018-azure
/usr/src/linux-headers-4.13.0-1018-azure