RFR(S): 8231949: [PPC64, s390]: Make async profiling more reliable

[Doerr, Martin]

Hi,

I'd like to make pd_get_top_frame_for_profiling more reliable on PPC64 and s390 as we have seen crashes in this function.

See bug for more details:
https://bugs.openjdk.java.net/browse/JDK-8231949

Webrev:
http://cr.openjdk.java.net/~mdoerr/8231949_get_top_frame_for_profiling/webrev.00/

Please review.

Best regards,
Martin