RFR: 8214761: Bug in parallel Kahan summation implementation

[Ian Graves]

8214761: Bug in parallel Kahan summation implementation

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Commit messages:
 - 8214761: Bug in parallel Kahan summation implementation

Changes: https://git.openjdk.java.net/jdk/pull/4674/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4674&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8214761
  Stats: 18 lines in 3 files changed: 11 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4674.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4674/head:pull/4674

PR: https://git.openjdk.java.net/jdk/pull/4674