RFR: 8349284: Make libExplicitAttach work on static JDK [v4]

[David Holmes]

On Mon, 10 Feb 2025 04:00:44 GMT, Jiangli Zhou <jiangli at openjdk.org> wrote:

>> This is similar to https://github.com/openjdk/jdk/pull/23431 change. It removes libjvm.so as a recorded dependency for libExplicitAttach.so by not explicitly link libExplicitAttach.so with libjvm.so at build time. To do that, it also changes libExplicitAttach.c to dynamically lookup the JNI_GetCreatedJavaVMs symbol then invokes the function using the obtained address. The change makes the test to work on both regular 'jdk' image and the 'static-jdk' image.
>> 
>> There are discussions in https://github.com/openjdk/jdk/pull/23431 comment thread among @dholmes-ora, @AlanBateman and myself. Based on my understanding, we are converging on the approach to fix just these few tests, and both @dholmes-ora and @AlanBateman are okay with that. So I'm sending out this PR for libExplicitAttach's fix as well.
>
> Jiangli Zhou has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused variables.

This seems a nice simplification to me too.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23500#pullrequestreview-2605315239