RFR (S): 8147910: Cache initial active_processor_count

[Thomas Schatzl]

Hi all,

  can I have reviews for this tiny change that adds an API to set the
initial active processor count at startup? It also adds that count to
the hs_err log file.

It is required to fix JDK-8161993.

CR:
https://bugs.openjdk.java.net/browse/JDK-8147910

Webrev:
http://cr.openjdk.java.net/~tschatzl/8147910/webrev/

Testing:
jprt, checking generated hs_err files using tasksel

Thanks,
  Thomas