RFR: 8369631: Assess and remedy any unsafe usage of the sr_semaphore Semaphore in the Posix signal code [v3]

[David Holmes]

> Replace the statically allocated "semaphore" with a pointer and lazily initialize it. I chose this approach as we already have a second Semaphore declared that way.
> 
> Testing:
> - tiers 1-3 sanity
> 
> Thanks.

David Holmes has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Fix misleading indent.
 - Merge branch 'master' into 8369631-sr_sem
 - Switch to DeferredStatic per Kim's request
 - 8369631: Assess and remedy any unsafe usage of the sr_semaphore Semaphore in the Posix signal code

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27762/files
  - new: https://git.openjdk.org/jdk/pull/27762/files/a8982e70..d200692a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27762&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27762&range=01-02

  Stats: 9608 lines in 240 files changed: 5571 ins; 3533 del; 504 mod
  Patch: https://git.openjdk.org/jdk/pull/27762.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27762/head:pull/27762

PR: https://git.openjdk.org/jdk/pull/27762