RFR (S): 7167254: Crash on OSX in Enumerator.nextElement() with compressed oops

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/7167254/webrev.00/

Crashes were reported for 64 bit VMs on OSX running in "compressed oops with base" mode. The crash is caused by a SIGBUS on a correctly aligned access to the first page of the heap which is used for implicit null checks. With this change hotspot on OSX expects either a SIGBUS or SIGSEGV for implicit null checks.

Roland.