RFR(XS): 8209939: [testbug][ppc] Test SafepointPollingPages fails after 8208499 with UseSIGTRAP on.

[Lindenmaier, Goetz]

Hi,

could I please get reviews for this tiny test fix?
http://cr.openjdk.java.net/~goetz/wr18/8209939-fixPollPageTest/01/

Per default, ppc does not use polling pages. It uses the trap instruction
to do the polling, which is faster. 
Setting -UseSIGTRAP makes ppc behave as other platforms.

Best regards,
  Goetz.