test_signal.rb: use standard fds
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41442 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_signal.rb: use standard fds
standard file descriptors instead of fd 3 and 4, which is not
available on Windows.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41442 b2dd03c8-39d4-4d8f-98ff-823fe69b080e