RFR: 8369631: Assess and remedy any unsafe usage of the sr_semaphore Semaphore in the Posix signal code [v2]

[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 incrementally with one additional commit since the last revision:

  Switch to DeferredStatic per Kim's request

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27762/files
  - new: https://git.openjdk.org/jdk/pull/27762/files/be87f8e9..a8982e70

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27762&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27762&range=00-01

  Stats: 20 lines in 1 file changed: 5 ins; 8 del; 7 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