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>

golang/tools,sshetty10/tools,dmitris/tools,argandas/tools,runcom/tools,magiccao/tools,josharian/tools,matryer/tools,josharian/tools,nicot/tools,runcom/tools,magiccao/tools,josharian/tools,argandas/tools,josharian/tools,springning/tools,cmars/tools,cmars/tools,matryer/tools,cw2018/tools,dmitris/tools,golang/tools,argandas/tools,matryer/tools,maddyonline/tools,dmitris/tools,matryer/tools,4ad/tools,syreclabs/go-tools,springning/tools,springning/tools,sshetty10/tools,nicot/tools,nicot/tools,syreclabs/go-tools,maddyonline/tools,nicot/tools,jdhenke/tools,syreclabs/go-tools,golang/tools,magiccao/tools,jdhenke/tools,cmars/tools,golang/tools,cw2018/tools,runcom/tools,cw2018/tools,cmars/tools,golang/tools,argandas/tools,cw2018/tools,springning/tools,glasser/golang-tools,sshetty10/tools,jdhenke/tools,runcom/tools,sshetty10/tools,4ad/tools,glasser/golang-tools,jdhenke/tools,glasser/golang-tools,maddyonline/tools,maddyonline/tools,magiccao/tools,glasser/golang-tools,dmitris/tools,syreclabs/go-tools,4ad/tools,syreclabs/go-tools,syreclabs/go-tools