RFR: 7903138: os.simpleArch is x64 for linux-riscv64 in @require context

[Feilong Jiang]

Set simpleArch to riscv64 when os.arch is riscv64

Tested on  Linux riscv64. With the patch, [test/hotspot/jtreg/compiler/vectorapi/TestMaskedMacroLogicVector.java](https://github.com/openjdk/jdk/blob/jdk-19%2B13/test/hotspot/jtreg/compiler/vectorapi/TestMaskedMacroLogicVector.java) was successfully skipped.

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Commit messages:
 - os.simpleArch is x64 for linux-riscv64 in @require context

Changes: https://git.openjdk.java.net/jtreg/pull/66/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=66&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903138
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/66.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/66/head:pull/66

PR: https://git.openjdk.java.net/jtreg/pull/66