cmd/vet: make TestTags pass on windows
cmd/vet: make TestTags pass on windows

Update golang/go#11811

Change-Id: I3d875acf58a015fa4cae16473a118ac8196b9b44
Reviewed-on: https://go-review.googlesource.com/12789
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

nicot/tools,matryer/tools,jdhenke/tools,argandas/tools,springning/tools,runcom/tools,argandas/tools,glasser/golang-tools,cmars/tools,glasser/golang-tools,syreclabs/go-tools,nicot/tools,jdhenke/tools,argandas/tools,jdhenke/tools,josharian/tools,runcom/tools,josharian/tools,argandas/tools,cmars/tools,golang/tools,golang/tools,golang/tools,cw2018/tools,magiccao/tools,glasser/golang-tools,cmars/tools,matryer/tools,matryer/tools,cw2018/tools,matryer/tools,syreclabs/go-tools,syreclabs/go-tools,josharian/tools,runcom/tools,magiccao/tools,runcom/tools,magiccao/tools,springning/tools,syreclabs/go-tools,syreclabs/go-tools,cmars/tools,josharian/tools,springning/tools,springning/tools,nicot/tools,jdhenke/tools,syreclabs/go-tools,nicot/tools,golang/tools,glasser/golang-tools,magiccao/tools,golang/tools,cw2018/tools,cw2018/tools