I spent a long time bisecting some largish program before realising
that failure was in fact coming from the child timing out due to
zjit_bisect.rb not clearing the stdout and stderr pipe.

Fix the pipe dead lock by redirecting to /dev/null. This sacrifices
the debug output during boot, but for that we also get to remove
a lot of code and the dependency on Open3.

Warning Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process.

https://docs.ruby-lang.org/en/master/Open3.html#method-i-popen3

Take care to avoid deadlocks. Output streams stdout and stderr have fixed-size buffers, so reading extensively from one but not the other can cause a deadlock when the unread buffer fills. To avoid that, stdout and stderr should be read simultaneously (using threads or IO.select).