lib9: fix Solaris build
lib9: fix Solaris build

In file included from src/lib9/utf/utfecpy.c:17:0:
src/lib9/utf/utfdef.h:28:0: error: "nil" redefined [-Werror]
In file included from src/lib9/utf/utfrrune.c:17:0:
src/lib9/utf/utfdef.h:28:0: error: "nil" redefined [-Werror]

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/63410043

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