RFR: 8349666: RISC-V: enable superwords tests for vector reductions

[Hamlin Li]

Hi,
Can you help to review this patch?

On riscv, some vector reduction intrinsics were already implemented, but they are not verified indeed. This patch is to enable these tests on riscv.

Thanks

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/23518/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23518&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349666
  Stats: 73 lines in 9 files changed: 64 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/23518.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23518/head:pull/23518

PR: https://git.openjdk.org/jdk/pull/23518