socket/extconf.rb: add -D
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40193 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
socket/extconf.rb: add -D
otherwize.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40193 b2dd03c8-39d4-4d8f-98ff-823fe69b080e