RFR: 8220606: Move ScavengeNMethods unlinking to unregister_nmethod

[Per Liden]

Looks good, but it looks like we could remove 
ScavengableNMethods::flush_nmethod() completely now. Don't need a new 
webrev if you decide to do that.

/Per

On 3/14/19 9:33 AM, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to move the removal of non-alive nmethods from 
> the scavengable nmethods list from the flush/purge phase into the 
> unregister_nmethod call.
> 
> This will prevent the GCs from scavenging dead nmethods.
> 
> http://cr.openjdk.java.net/~stefank/8220606/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8220606
> 
> Tested with tier1-3.
> 
> Thanks,
> StefanK