netbsd-arm needs the same override to the alignment function as
openbsd-arm. This fixes the TestPassFD failure.

Update golang/go#24771

Change-Id: Ib124fc776f6e2e3b3932784365c2bd3944523a52
Reviewed-on: https://go-review.googlesource.com/c/164458
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>