RFR: Simpler obj equals barrier for C2

[Roman Kennke]

> 
>> There's 3 affected intrinsics:
>> - isInterrupted: this one did not actually change
>> - subtype-check: this seems likely to trigger, and in-fact I have seen
>> it trigger because I had a bug in my barrier
>> - aes-crypt: this one will likely not trigger by the test-suite, but by
>> specjvm. I'm running it now.
> 
> java -XX:-TieredCompilation -XX:+CompileTheWorld -XX:+UseShenandoahGC -version
> 
> will stress test everything.

Alright, that failed in CipherBlockChaining::decrypt() :-)

>> WBs work in all other places, and produces the memphis that it needs,
>> afaik. I don't really understand why it wouldn't here.
> 
> In other places, parsing builds the control flow and adds the phis. With
> intrinsics, we add explicit control flow and so we must add phis
> ourselves because nothing else does it for us.

The next best thing to try is to do resolve_for_obj_equals(a, b)
approach, right? Or is there a way to get this simpler/better(IMO) API
to work without too much messing about?

Roman