RFR: 8344239: runtime/cds/appcds/jigsaw/addmods/AddmodsOption.java fails on x64 with -Xmixed

[Calvin Cheung]

A simple test fix to correct the setting of the `isJVMCISupported` boolean variable.

Ran the test successfully on linux-x64 with and without the `-Xmixed` VM option.

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Commit messages:
 - 8344239: runtime/cds/appcds/jigsaw/addmods/AddmodsOption.java fails on x64 with -Xmixed

Changes: https://git.openjdk.org/jdk/pull/22226/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22226&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344239
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22226.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22226/head:pull/22226

PR: https://git.openjdk.org/jdk/pull/22226