RFR: 8242240: JfrStacktrace_lock rank not special enough

[Erik Österlund]

Hi,

After a ZGC event was added, we sometimes acquire the JfrStacktrace_lock 
(special rank) when the CodeCache_lock (special rank)
is held. This leads to an assertion error. My proposed solution is to 
make the JfrStacktrace_lock even more special (special - 1).
Special locks are the new normal.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8242240

Webrev:
http://cr.openjdk.java.net/~eosterlund/8242240/webrev.00/

Thanks,
/Erik