RFR: 8302189: Mark assertion failures noreturn [v2]

[Kim Barrett]

> Also 8302799: Refactor Debugging variable usage for noreturn crash reporting

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  make Debugging::_enabled a nesting counter

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12845/files
  - new: https://git.openjdk.org/jdk/pull/12845/files/ca68e500..f296ab62

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12845&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12845&range=00-01

  Stats: 10 lines in 2 files changed: 1 ins; 4 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/12845.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12845/head:pull/12845

PR: https://git.openjdk.org/jdk/pull/12845