RFR: Fix counter inccurate when creating platform/virtual thread by Thread…

[Miao Zheng]

Fix counter inccurate when creating platform/virtual thread by ThreadBuilder using mutiple threads

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Commit messages:
 - Fix counter inccurate when creating platform/virtual thread by ThreadBuilder using mutiple threads

Changes: https://git.openjdk.java.net/loom/pull/45/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=45&range=00
  Stats: 12 lines in 1 file changed: 10 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/loom/pull/45.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/45/head:pull/45

PR: https://git.openjdk.java.net/loom/pull/45