Assert poisoning initialization before os memory subsystem

[Thomas Schatzl]

Hi Thomas,

  the change "JDK-8191101: Show register content in hs-err file on
assert" added some code that initializes some memory page for
retrieving the register context on assert failure.

This reserves, commits and mprotects a single VM page.

The problem is that this occurs before the os subsystem completely
initialized itself, causing issues if not guarded against in the commit
code - i.e. if UseNUMA is enabled, the VM did not get a chance to
initialize the NUMA subsystem (even if it just disables it).

Obviously all os implementations guard already against this (because
they do not crash; during review of JDK-8213827 we temporarily removed
this guard and hence noticed this), and from a functionality pov NUMA
initialization is not needed for this feature.

However I was wondering whether it is really necessary to do this
assert poisoning setup before the os::init_2 call. Do you have any
recollection why the poisoining (needs to?) occurs that early?

It looks like a bit of an ugly wart to use the os component without
having it completely initialized.

Thanks,
  Thomas :P