we're not changing the O_NONBLOCK bit. F_SETFL is an expensive
operation since it needs to affect all processes with the same
file object.
The patch is written by Eric Wong. [ruby-core:35556]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@31238 b2dd03c8-39d4-4d8f-98ff-823fe69b080e