RFR: 8295009: RISC-V: Interpreter intrinsify Thread.currentThread()

[Yadong Wang]

Calling intrinsic version of Thread.currentThread() in interpreter is ~30% faster on the Unmatched board:
Before:
Benchmark Mode Cnt Score Error Units
MyBenchmark.testCurrentThread avgt 5 4665.765 ± 212.906 ns/op
After:
Benchmark Mode Cnt Score Error Units
MyBenchmark.testCurrentThread avgt 5 3381.415 ± 223.005 ns/op

Tier1 and jdk_loom have been tested on unmatched.

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Commit messages:
 - 8295009: RISC-V: Interpreter intrinsify Thread.currentThread()

Changes: https://git.openjdk.org/jdk/pull/10709/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10709&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295009
  Stats: 15 lines in 4 files changed: 11 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10709.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10709/head:pull/10709

PR: https://git.openjdk.org/jdk/pull/10709