RFR: 8283849: AsyncGetCallTrace may crash JVM on guarantee [v4]

[Jaroslav Bachorik]

> A gist of the fix is to allow relaxed special handling of code blob lookup when done for ASGCT. 
> 
> Currently, a guarantee will fail when we happen to hit a zombie method which is still on stack. While this would indicate a serious error for the normal execution flow, in case of ASGCT being in progress when the executing thread can be expected at any possible method this is something which may happen and we really should not take the profiled JVM down due to it.
> 
> <hr>
> Unfortunately, I am not able to create a simple reproducer for the crash other that testing in our production where the crash is happening sporadically.
> However, thanks to @parttimenerd and his [ASGCT stress test](https://github.com/parttimenerd/asgct2-tester.git) the problem can be reproduced quite reliably.
> 
> <br><br>
> 
> _Note: This is a followup PR for #8061_

Jaroslav Bachorik has updated the pull request incrementally with one additional commit since the last revision:

  AGCT -> ASGCT

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8549/files
  - new: https://git.openjdk.java.net/jdk/pull/8549/files/71e5a919..caf43e39

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8549&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8549&range=02-03

  Stats: 15 lines in 3 files changed: 4 ins; 8 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8549.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8549/head:pull/8549

PR: https://git.openjdk.java.net/jdk/pull/8549