hurd: Add no-op version of __res_enable_icmp [BZ #24047]

Mach does not support IP_RECVERR, so replace this function with a
stub in a sysdeps override for Hurd.

This fixes commit 08504de7
("resolv: Enable full ICMP errors for UDP DNS sockets [BZ #24047]").

Reviewed-by: Carlos O'Donell <carlos@redhat.com>