[jdk11u-dev] RFR: 8248666: AArch64: Use THREAD_LOCAL instead of __thread

[Reka Kovacs]

Not a clean backport. Original patch used a macro called THREAD_LOCAL, this backport uses THREAD_LOCAL_DECL. THREAD_LOCAL_DECL was renamed to THREAD_LOCAL by [JDK-8230877](https://bugs.openjdk.java.net/browse/JDK-8230877) in JDK 14. Testing: tier1.

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Commit messages:
 - Backport 2f8653fbf0f4ed2ab0e40b2bb541ef2eff913469

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/262/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=262&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248666
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/262.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/262/head:pull/262

PR: https://git.openjdk.java.net/jdk11u-dev/pull/262