ld: allow relocations pointing at ELF .bss symbols
ld: allow relocations pointing at ELF .bss symbols

R=r, r2
CC=golang-dev
http://codereview.appspot.com/3710042

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