RFR: 8335358: [premain] Explore alternative ways to trigger the end of training run [v8]

[Mat Carter]

> AOT training can be ended using either
> 
> - -XX: AOTEndTrainingOnMethodEntry =Hello.someMethod [same syntax as CompileOnly]
> - -XX: AOTEndTrainingOnMethodEntry =Hello.someMethod,Hello.someOtherMethod,count=42
> - jcmd <pid> AOT.end_training
> 
> supports arm64 and x64
> 
> note: the AOTEndTrainingOnMethodEntry is ignored when CDSPreImage is specified; this is needed as the phase2 forked java process is passed all phase1 flags along with the -XX:CDSPreImage, but we don't want to run the trigger code in this phase (there may be a better way to handle this state or simply remove the flag from the forked process)
> 
> JBS Issue: https://bugs.openjdk.org/browse/JDK-8335358

Mat Carter has updated the pull request incrementally with one additional commit since the last revision:

  Clear the method flags before committing to the archive, so that we don't require 'trigger' methods outside of training

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

Changes:
  - all: https://git.openjdk.org/leyden/pull/21/files
  - new: https://git.openjdk.org/leyden/pull/21/files/f9901e5e..d41acfcd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=21&range=07
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=21&range=06-07

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/leyden/pull/21.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/21/head:pull/21

PR: https://git.openjdk.org/leyden/pull/21