This copies over some files from the main repo to make the
GOOS=openbsd GOARCH=arm go install and go test -c work.

No clue whether it actually works or not, though. We don't have
builders anymore for this port.

But once this compiles, we'll at least be able to use constants from
the x/sys/unix package from x/net without regressing x/net's support
for openbsd/arm. (If anybody uses openbsd/arm)

Fixes golang/go#10826

Change-Id: Id821e2011bcd2d3720652be44ac09e4ce4d2a3a3
Reviewed-on: https://go-review.googlesource.com/54053
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Joel Sing <joel@sing.id.au>