RFR(xxs): 8210314: [aix] NMT does not show "Safepoint" memory type

[Thomas Stüfe]

Hi all,

may I please have reviews for this small, AIX-only change.

cr: http://cr.openjdk.java.net/~stuefe/webrevs/8210314-aix-NMT-does-not-show-safepoint-memory/webrev.00/webrev/

bug: https://bugs.openjdk.java.net/browse/JDK-8210314

On AIX, we have our own initialization for the safepoint mechanism. We
missed registering the polling page with NMT, which the generic code
path did. This patch adds that.

Side note:

We are different for two reasons. One, on ppc we use per default
SIGTRAP for safepoint signalling, which can be switched off though.
Second, on AIX, we cannot use os::reserve_memory() to obtain a polling
page since that memory may not protectable (if it uses sysV shmat).
Hence, the AIX specific coding.

Best Regards, Thomas