cmd/link: add testdata/pclntab.6 (fix build)
cmd/link: add testdata/pclntab.6 (fix build)

Sorry, "hg status" hides .6 files by default.
We should probably fix that.

TBR=iant
CC=golang-codereviews
https://codereview.appspot.com/55290043

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