os: use a different symbol from syscall in mkunixsignals.sh.
os: use a different symbol from syscall in mkunixsignals.sh.

Open is more likely to be present than Syscall.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4645073

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