io.c: suppress unused variable warnings
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
io.c: suppress unused variable warnings
when spawnv is available but fork is not.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e