(urgent) RFR: 8148771: os::active_processor_count() returns garbage which causes VM to crash

[David Holmes]

This is a backout of the fix for JDK-8147906 which changes the GC to use 
active_processor_count() during initialization. Some systems with 
aggressive power management can report continually varying numbers of 
available processors, via sched_getaffinity, and it seems the GC code 
can not tolerate that. So we hg backout JDK-8147906 and revert to using 
processor_count() again. We will then look at how to address this going 
forward.

Bug: https://bugs.openjdk.java.net/browse/JDK-8148771

webrev http://cr.openjdk.java.net/~dholmes/8148771/webrev/

Thanks,
David