RFR: JDK-8211241: Missing obj equals in TemplateTable::fast_aldc

[Roman Kennke]

TemplateTable::fast_aldc compares the just-loaded reference with
Universe::the_null_sentinel. If it really is that null-sentinel, we may
get a false negative (with GCs like Shenandoah that allow both
from-space and to-space copies of an object to be around), and thus skip
NULL-ing the ref. In other words, it would allow to get
the-null-sentinel out into the wild as oop which can cause subtle and
not-so-subtle bugs.

Fix is easy, call cmpoop() which re-routes through GC-interface for GCs
that need it:

http://cr.openjdk.java.net/~rkennke/JDK-8211241/webrev.00/

Testing: hotspot/jtreg:tier1

Ok?

Roman