It was passing options to the test harness rather than ruby(1).

Find ZJIT options in RUN_OPTS/SPECOPTS and put new ones from the bisection script
there too.

ZJIT: Improve zjit_bisect.rb

1. The command name in the help message is outdated.
2. When the command failed by itself, the message can be clearer.

I spent a long time bisecting some largish program before realizing
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 deadlock 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.

Also add a check in the bisect script that can assign blame to the HIR
optimizer.