RFR: 8314243: Make VM_Exit::wait_for_threads_in_native_to_block wait for user threads time configurable [v3]

[Jiangli Zhou]

> CSR: https://bugs.openjdk.org/browse/JDK-8314305

Jiangli Zhou has updated the pull request incrementally with one additional commit since the last revision:

  Incorporate David Holmes' UserThreadWaitAttemptsAtExit flag doc edit suggestion.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16591/files
  - new: https://git.openjdk.org/jdk/pull/16591/files/8a02e7e5..bfb35580

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16591&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16591&range=01-02

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/16591.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16591/head:pull/16591

PR: https://git.openjdk.org/jdk/pull/16591