Shrinks cmd/go's text segment by 0.9%.

   text	   data	    bss	    dec	    hex	filename
6447148	 231643	 146328	6825119	 68249f	go.before
6387404	 231643	 146328	6765375	 673b3f	go.after

Change-Id: I431e8482dbb11a7c1c77f2196cada43d5dad2981
Reviewed-on: https://go-review.googlesource.com/30817Reviewed-by: Austin Clements <austin@google.com>