cmd/gc: silence clang warning
cmd/gc: silence clang warning

This code is only built when you run 'make' in cmd/gc,
not in all.bash.

R=golang-dev, jsing, iant
CC=golang-dev
https://codereview.appspot.com/19160043

sanjosh/sanjos100-tipc,d0f/go-zh,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,d0f/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof