RFR: 7903920: Support building jtreg on FreeBSD

[Jan Lahoda]

On Sat, 14 Dec 2024 10:48:09 GMT, snake66 <duke at openjdk.org> wrote:

> On FreeBSD we need to use GNU gmake instead of the BSD make program.

Although I am not really an expert, but since @magicus approved, looks sensible to me.

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Marked as reviewed by jlahoda (Lead).

PR Review: https://git.openjdk.org/jtreg/pull/237#pullrequestreview-2581911771