Log Message:
Check for hes_getmailhost before trying to call it. It's not in the libc
hesiod, and it looks as if it's a deprecated feature.

This in turn will make the mail notify tool not understand Hesiod
mailserver records on NetBSD and probably anyone else with a builtin
hesiod. If anyone really really wants that functionality, set
PREFER.hesiod=pkgsrc and let it build and link to the pkgsrc hesiod
library...

Fixes the build of zephyr.