RFR: 8290164: compiler/runtime/TestConstantsInError.java fails on riscv

[Feilong Jiang]

compiler/runtime/TestConstantsInError.java fails on riscv with the following error:


Execution failed: `main' threw exception: java.lang.RuntimeException: 'made not entrant' found in stdout


Similar to AArch64, RISCV64 does not patch C1 compiled code (see [JDK-8223613](https://bugs.openjdk.org/browse/JDK-8223613)). So we should add `Platform.isRISCV64` too for the test.

According to [JDK-8246494](https://bugs.openjdk.org/browse/JDK-8246494), `vm.flagless` will be excluded from runs w/ any other X / XX flags passed via -vmoption / -javaoption. We added the `-Xmx` option for all jtreg tests, so the failure was not aware before.

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Commit messages:
 - Add Platform.isRISCV64 for compiler/runtime/TestConstantsInError.java

Changes: https://git.openjdk.org/jdk/pull/9463/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9463&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290164
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/9463.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9463/head:pull/9463

PR: https://git.openjdk.org/jdk/pull/9463