[14] RFR (S): 8234401: ConstantCallSite may stuck in non-frozen state

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8234401/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8234401

ConstantCallSite has a ctor which deliberately leaks partially 
initialized instance into user code. isFrozen is declared final and if 
user code is obstinate enough, it can end up with non-frozen state 
embedded into the generated code. It manifests as a ConstantCallSite 
instance which is stuck in non-frozen state.

I switched isFrozen from final to @Stable, so non-frozen state is never 
constant folded. Put some store-store barriers along the way to restore 
final field handling.

I deliberately stopped there (just restoring isFrozen final field 
behavior). Without proper synchronization, there's still a theoretical 
possibility of transiently observing a call site in non-frozen state 
right after ctor is over. But at least there's no way anymore to 
accidentally break an instance in such a way it becomes permanently 
unusable.

PS: converted CallSite.target to final along the way and made some other 
minor refactorings.

Testing: regression test, tier1-2

Best regards,
Vladimir Ivanov