RFR: 7903920: Support building jtreg on FreeBSD

[Jonathan Gibbons]

On Thu, 23 Jan 2025 20:06:27 GMT, snake66 <duke at openjdk.org> wrote:

>> Okay, people have apparently varying opinions on this. :) Don't want to put you in a "damned if you do, damned if you don't" situation, so just ignore my comment and go with your solution.
>
> I don't have any strong opinions about this, but for FreeBSD's part it would actually be slightly better to let the shell find the binaries in $PATH. But it's not important for my progress now, so I figured I'd deal with it if it comes up :)

Maybe the concern is becoming obsolete, but the general design focus of this and similar scripts was to lock down everything, and avoid any variation that might occur as a result of individuals setting non-standard values for PATH and similar path-related variables -- CLASSPATH anyone?

But, a reasonable compromise would be to limit the use of `which` to this file (`Defs.gmk`) and maybe to within suitable `ifeq ($(SYSTEM_UNAME), FreeBSD)` constructs.

That all being said, I would defer to the expertise and style-advice of folk like @magicus on the Build team,  but with some amount of caveat for overall style consistency, as much as is reasonable.

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PR Review Comment: https://git.openjdk.org/jtreg/pull/237#discussion_r1929341033