Fix compilation on systems that do not define HOST_NAME_MAX

Fix compilation on systems that do not define HOST_NAME_MAX

On FreeBSD at least, HOST_NAME_MAX is not defined and we need to
use sysconf() to get the value at runtime instead.
Based on a work done by @RvdE to make the recursor compile on
FreeBSD (many thanks!).

(cherry picked from commit 4c990a1b82e091d887d873c7da5254de84aabebb)
(cherry picked from commit 5c21b47fbc35ddcb8d939eb8541c6c3bad1080a8)