RFR(xs): 8202772: NMT erroneously assumes thread stack boundaries to be page aligned

[Thomas Stüfe]

Dear all,

may I please have reviews for this fix, which - for now - disables
thread stack tracking for NMT on AIX.

Bug: https://bugs.openjdk.java.net/browse/JDK-8202772
Webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8202772-NMT-erroneously-assumes-thread-stack-boundaries-to-be-page-aligned/webrev.00/webrev/

On AIX, we have two problems:

- NMT assumes stack boundaries to be page aligned. This is wrong but
on all platforms other than AIX does not matter.
- the way mincore() is used to read residency of pages needs to be
adapted since on AIX, os::vm_page_size() is not necessarily the page
size used by mincore() - which is quite dangerous.

Since JDK-8204552 was added to deal with the first point, it makes
sense to wait until that issue is finished. Until then, I'd like to
disable thread stack recognition in NMT for AIX. We can revisit this
topic again once we can spare time for it and JDK-8204552 has been
done.