RFR: 8371698: ZGC: Call GTEST_SKIP when OS is unsupported

[Martin Doerr]

On Mon, 17 Nov 2025 11:12:36 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> We have a ZGC-specific test fixture for our gtests. This fixture bails out if the OS is unsupported. In addition to that, all tests need to bail out as well. It turns out that we missed this bail-out in one of our tests.
> 
> I propose that we perform a stronger bail-out in the test fixture to make this error less likely to happen in the future.

This looks good and solves the issue. Thanks for improving it!

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Marked as reviewed by mdoerr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28348#pullrequestreview-3476523010