RFR(XS): 8027964: Adapt PPC to 6843347: Boundary values in some public GC options cause crashes

[Lindenmaier, Goetz]

Hi,

Please review this change.  It's really small, ppc only and required by the last
update of the ppc staging repository.

http://cr.openjdk.java.net/~goetz/webrevs/8027964/

Best regards,
  Goetz Lindenmaier