RFR: 8308347: [s390x] build broken after JDK-8304913

[Amit Kumar]

s390x needs to be recognised as `S390`. After [JDK-8304913](https://bugs.openjdk.org/browse/JDK-8304913) during build I was getting this PluginException: 

jdk.tools.jlink.plugin.PluginException: ModuleTarget is malformed: No enum constant jdk.internal.util.Architecture.S390X
        at jdk.jlink/jdk.tools.jlink.builder.DefaultImageBuilder.storeFiles(DefaultImageBuilder.java:181)
        at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.storeFiles(ImagePluginStack.java:486)
        at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.writeImage(ImageFileCreator.java:168)
        at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.create(ImageFileCreator.java:100)
        at jdk.jlink/jdk.tools.jlink.internal.JlinkTask$ImageHelper.retrieve(JlinkTask.java:860)
        at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.operate(ImagePluginStack.java:194)
        at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.createImage(JlinkTask.java:423)
        at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.run(JlinkTask.java:286)
        at jdk.jlink/jdk.tools.jlink.internal.Main.run(Main.java:56)
        at jdk.jlink/jdk.tools.jlink.internal.Main.main(Main.java:34)


Builds tested :`fastdebug, release`.

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/14043/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14043&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308347
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14043.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14043/head:pull/14043

PR: https://git.openjdk.org/jdk/pull/14043