ld: remove duplicate bss definitions
ld: remove duplicate bss definitions

The EXTERN lines in elf.h already define these.
That's not a problem for most C compilers, but
apparently it is for some copies of the OS X linker.

Fixes issue 2167.

R=golang-dev, iant
CC=golang-dev
http://codereview.appspot.com/4936044

sanjosh/sanjos100-tipc,npe9/noahevans-go9,rdp/rogerpack2005-golang,bryanxu/go-zh,npe9/noahevans-go9,npe9/noahevans-go9,rdp/rogerpack2005-golang,d0f/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,Triskite/willstone-goclone,mhennings/marcohennings-go,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,scirelli/scirelli-go,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,webfd/go-zh,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,webfd/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,scirelli/scirelli-go,d0f/go-zh,Triskite/willstone-goclone,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,npe9/noahevans-go9,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,bryanxu/go-zh,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,webfd/go-zh,mhennings/marcohennings-go,bryanxu/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,rflanagan/reginaldflanagan-project1,rflanagan/reginaldflanagan-project1,d0f/go-zh,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,scirelli/scirelli-go,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,npe9/noahevans-go9,sanjosh/sanjos100-tipc,d0f/go-zh,mhennings/marcohennings-go,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,scirelli/scirelli-go,Triskite/willstone-goclone,webfd/go-zh,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,webfd/go-zh,d0f/go-zh,npe9/noahevans-go9,npe9/noahevans-go9,bryanxu/go-zh,sanjosh/sanjos100-tipc,scirelli/scirelli-go,Triskite/willstone-goclone,d0f/go-zh,npe9/noahevans-go9