[jdk21u] RFR: 8325194: GHA: Add macOS M1 testing

[George Adams]

On Tue, 6 Feb 2024 14:23:12 GMT, George Adams <gdams at openjdk.org> wrote:

> Now that macOS M1 executors are [available in GitHub actions](https://github.blog/changelog/2024-01-30-github-actions-introducing-the-new-m1-macos-runner-available-to-open-source/) it makes sense to move the build to run on M1 (rather than cross-compiled) and also enable testing on the platform.

I'm surprised the `$(realpath bootjdk/jdk)` change is breaking things here. CC @shipilev as I know you've looked at this codebase recently, do I need to backport something else first?

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PR Comment: https://git.openjdk.org/jdk21u/pull/435#issuecomment-1929867477