RFR(xxs): 8241395: Factor out platform independent code for os::xxx_memory_special()

[Thomas Stüfe]

Hi,

may I please have reviews for this little cleanup.

A while ago we factored out platform independent behavior for
os::reserve_memory() and friends to os.cpp and relegated platform
dependent code to os::pd_reserve_memory() etc. This change does the same
for os::reserve_memory_special() and os::release_memory_special().

Only Linux and Windows are affected since only they have meaningful
implementations for UseLargePages.

It also adds a small comment about the NMT Tracker object.

In addition it asserts - now for all platforms, it used to do this only on
Linux - that if both requested address and alignment are given to
os::reserve_memory_special() the requested address should at least be
aligned to the given alignment (the arguments should be mutually exclusive
and I plan to clean this up further).

Issue: https://bugs.openjdk.java.net/browse/JDK-8241395
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8241395-refactor-reserve-memory-special/webrev.00/webrev/

Thanks, Thomas