dashboard/buildlet: add NetBSD-amd64 to Makefile
dashboard/buildlet: add NetBSD-amd64 to Makefile

Update golang/go#8643

Change-Id: Ie60b87c447180a2a7f2411fcf8fece8035ddfa9d
Reviewed-on: https://go-review.googlesource.com/2602
Reviewed-by: Benny Siegert <05f4aee36fd25d0de2a07789fd6e73398db492cc@gmail.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

evandbrown/build,proppy/build,proppy/build,evandbrown/build,golang/build,golang/build,golang/build,evandbrown/build,proppy/build,proppy/build,golang/build