cmd/nm: disable TestNM on darwin, linux and solaris
cmd/nm: disable TestNM on darwin, linux and solaris

Update issue 7829

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://codereview.appspot.com/89810043

firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang