RFR: 8275730: Relax memory constraint on MultiThreadedRefCounter

[Zhengyu Gu]

It is just an atomic counter, only needs atomic guarantee.

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Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/6069/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6069&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275730
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6069.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6069/head:pull/6069

PR: https://git.openjdk.java.net/jdk/pull/6069