Port recent AIX-related developments done by SAP to the OpenJDK. These are a number of changes, among others:

- Prepares the VM for running on PASE. PASE is an AIX-like runtime environment for iSeries servers. Note that PASE support is not yet complete.
- Remove remnants from Linux port on AIX (AIX port was originally forked from Linux).
- Rework and extend the libperfstat wrapper and separate it from the os layer.
- Switch from kernel thread ids to pthread ids for OSThread::_thread_id.
- Introduce a number of new switches, AIX specific, to control behaviour of the AIX layer.
- Remove Use16MPages switch because we pulled support for that variant. (note that the normal mode of operation on AIX is 64k paged java heap, unless the OS is very old).
- Reworked the multipage support probing in the os layer