DragonflyBSD: add ENOMEDIUM and EASYNC
DragonflyBSD: add ENOMEDIUM and EASYNC

These errno's are defined in <sys/errno.h> on DragonFlyBSD.

Signed-off-by: Levente Kurusa <855c91457b18bc4d5995dfa202dd377c2433de4a@acm.org>

rust-lang-nursery/libc,rust-lang/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang/libc