IR improperly masks errors in defined-guarded conditional

[headius]

This code raises NotImplementedError running under the JIT, but completes successfully (incorrectly) under IR interpreter:

if defined?(Process::RLIMIT_AS)
  Process.rlimit # This should raise
end

I have not started examining the IR this is producing, nor why it works properly in JIT.

[headius]

Tagging @subbuss and @enebo.

[headius]

@subbuss Very nice :-) I was going to circle back to this after today's audit, but yay for having it fixed!