[jdk26u] RFR: 8373630: r18_tls should not be modified on Windows AArch64

[Saint Wesonga]

Clean backport

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Commit messages:
 - Backport a0dd66f92d7f8400b9800847e36d036315628afb

Changes: https://git.openjdk.org/jdk26u/pull/4/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk26u&pr=4&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373630
  Stats: 23 lines in 1 file changed: 23 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk26u/pull/4.diff
  Fetch: git fetch https://git.openjdk.org/jdk26u.git pull/4/head:pull/4

PR: https://git.openjdk.org/jdk26u/pull/4