[11u] RFR: 8173658: JvmtiExport::post_class_unload() is broken for non-JavaThread initiators

[Lindenmaier, Goetz]

Hi

I am downporting this for parity with 11.0.10-oracle.
I had to resolve and adapt the code, e.g. I replaced MutexLocker by MutexLockerEx.

http://cr.openjdk.java.net/~goetz/wr20/8173658-post_class_unload-jdk11/01/

Please review.

https://bugs.openjdk.java.net/browse/JDK-8173658
https://hg.openjdk.java.net/jdk/jdk/rev/4774b50671ed

Best regards,
  Goetz.