RFR: 8268638: semaphores of AsyncLogWriter may be broken when JVM is exiting.

[Xin Liu]

All 3 semaphores used by AsyncLogWriter are static member data. C++ runtime on
MacOS deletes them. Currently, AsyncLog Thread doesn't exit. Semaphore_wait/signal
returns with KERN_INVALID_NAME(15) if those semaphore are destroyed. 

This patch change those to regular data members. This prevents from deleting.

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Commit messages:
 - 8268638: semaphores of AsyncLogWriter may be broken when JVM is exiting.

Changes: https://git.openjdk.java.net/jdk/pull/4479/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4479&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268638
  Stats: 28 lines in 3 files changed: 10 ins; 5 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4479.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4479/head:pull/4479

PR: https://git.openjdk.java.net/jdk/pull/4479