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

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang