RFR: 8359472: JVM crashes when attaching a dynamic agent before JVMTI_PHASE_LIVE [v15]

[Francesco Andreuzzi]

> In this PR I add a check to prevent debug builds to crash when an agent tries to attach while the JVM is not in live phase.
> 
> Passes tier1 and tier2 (fastdebug).

Francesco Andreuzzi has updated the pull request incrementally with one additional commit since the last revision:

  empty stderr

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27766/files
  - new: https://git.openjdk.org/jdk/pull/27766/files/925f9fc8..60d6fdff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27766&range=14
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27766&range=13-14

  Stats: 8 lines in 1 file changed: 2 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27766.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27766/head:pull/27766

PR: https://git.openjdk.org/jdk/pull/27766