[8u] RFA 8153267: nmethod's exception cache not multi-thread safe

[David Buck]

Hi!

Please approve the following backport of JDK-8153267 from 9 to 8u:

8153267 bug report:   https://bugs.openjdk.java.net/browse/JDK-8153267
8u backport webrev:   http://cr.openjdk.java.net/~dbuck/8153267.0_jdk8u/
code review thread: 
http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2017-April/025944.html

Cheers,
-Buck