Here's a snippet from the task's stdout log:

[2023-05-16T16:57:26,258Z] [buildjdk] Creating interim jimage
[2023-05-16T16:57:28,707Z] jdk.tools.jlink.plugin.PluginException: ModuleTarget is malformed: No enum constant jdk.internal.util.Architecture.ARM
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.builder.DefaultImageBuilder.storeFiles(DefaultImageBuilder.java:181)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.storeFiles(ImagePluginStack.java:486)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.writeImage(ImageFileCreator.java:168)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.create(ImageFileCreator.java:100)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask$ImageHelper.retrieve(JlinkTask.java:860)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.operate(ImagePluginStack.java:194)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.createImage(JlinkTask.java:423)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.run(JlinkTask.java:286)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.Main.run(Main.java:56)
[2023-05-16T16:57:28,708Z] at jdk.jlink/jdk.tools.jlink.internal.Main.main(Main.java:34)
[2023-05-16T16:57:28,710Z] Error: jdk.tools.jlink.plugin.PluginException: ModuleTarget is malformed: No enum constant jdk.internal.util.Architecture.ARM
[2023-05-16T16:57:28,711Z] java.io.IOException: jdk.tools.jlink.plugin.PluginException: ModuleTarget is malformed: No enum constant jdk.internal.util.Architecture.ARM
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.writeImage(ImageFileCreator.java:173)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.create(ImageFileCreator.java:100)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask$ImageHelper.retrieve(JlinkTask.java:860)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.operate(ImagePluginStack.java:194)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.createImage(JlinkTask.java:423)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.JlinkTask.run(JlinkTask.java:286)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.Main.run(Main.java:56)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.Main.main(Main.java:34)
[2023-05-16T16:57:28,712Z] Caused by: jdk.tools.jlink.plugin.PluginException: ModuleTarget is malformed: No enum constant jdk.internal.util.Architecture.ARM
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.builder.DefaultImageBuilder.storeFiles(DefaultImageBuilder.java:181)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.ImagePluginStack.storeFiles(ImagePluginStack.java:486)
[2023-05-16T16:57:28,712Z] at jdk.jlink/jdk.tools.jlink.internal.ImageFileCreator.writeImage(ImageFileCreator.java:168)
[2023-05-16T16:57:28,712Z] ... 7 more


I looked at the change sets in jdk-21+23-1959-tier5 and there's
nothing obvious that would have caused this build failure.

Update: The actual first failure was in jdk-21+23-1950-tier5 and I
missed it earlier. That build-ID does contain the fix for JDK-8304913
which is the root cause of this failure.