go.tools/playground/socket: add support for Native Client on arm
go.tools/playground/socket: add support for Native Client on arm

LGTM=minux
R=adg, minux
CC=golang-codereviews
https://golang.org/cl/110900043

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