For all supported platforms (386, amd64, arm).

Note that this doesn't update whole `unix` package for these platforms.

Change-Id: I0a66f8403f704c6328000ffc9f238989c22936d2
GitHub-Last-Rev: 14fd451964abcfacdb94dca3dc41742bacd0f732
GitHub-Pull-Request: golang/sys#21
Reviewed-on: https://go-review.googlesource.com/c/143542Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>