RFR: 8264032: Improve thread safety of Runtime.version()

[Andrey Turbanov]

Avoid double-read non volatile static field

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Commit messages:
 - [PATCH] Thread-safe initialization of Runtime.version

Changes: https://git.openjdk.java.net/jdk/pull/2691/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2691&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264032
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2691.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2691/head:pull/2691

PR: https://git.openjdk.java.net/jdk/pull/2691