RFR: 8212663: Remove conservative at_safepoint assert when JFR writes type sets during class unloading

[Erik Österlund]

Hi,

JFR writes type sets during class unloading. It currently asserts this 
is done in a safepoint. But in fact, it suffices that it is done by a 
single thread. This assert needs to be relaxed for concurrent class 
unloading.

Webrev:
http://cr.openjdk.java.net/~eosterlund/8212663/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8212663

Thanks,
/Erik