[jdk24u] RFR: 8351933: Inaccurate masking of TC subfield decrement in ForkJoinPool

[Dmitry Chuyko]

This is a clean backport of a tiny ForkJoinPool change that corrects the TC subfield masking.

-------------

Commit messages:
 - Backport fed34e46b89bc9b0462d9b5f5e5ab5516fe18c6e

Changes: https://git.openjdk.org/jdk24u/pull/148/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk24u&pr=148&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351933
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk24u/pull/148.diff
  Fetch: git fetch https://git.openjdk.org/jdk24u.git pull/148/head:pull/148

PR: https://git.openjdk.org/jdk24u/pull/148