[8u] RFR(S): 8050972: Concurrency problem in PcDesc cache

[Vladimir Kozlov]

8u (8u40) backport request. The fix was pushed into jdk9 yesterday and 
nightly testing shows no related problems.

Changes from jdk9 applied to 8u without conflicts.

http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/82cd02bbfc3a
http://cr.openjdk.java.net/~goetz/webrevs/8050972-pcDescConc/webrev-01/ 
https://bugs.openjdk.java.net/browse/JDK-8050972

Thanks,
Vladimir