cmd/ld: refine test for history stack pop (fix Windows build)
cmd/ld: refine test for history stack pop (fix Windows build)

This should fix the Windows build, or at least
what's breaking it at the moment.

Fixes issue 5904.

TBR=golang-dev
CC=golang-dev
https://codereview.appspot.com/11519044

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