[crac] RFR: 8361090: [CRaC] Make dev engines less confusing

[Timofei Pushkin]

On Tue, 1 Jul 2025 08:49:29 GMT, Radim Vansa <rvansa at openjdk.org> wrote:

>> - Makes `pauseengine` Linux-only since it is not fully implemented on MacOS and Windows
>>    - Also moves `criuengine` sources from `unix` to `linux` directory since it only supports Linux anyway
>> - Makes `simengine` and `pausengine` report errors and status in more details
>
> src/java.base/linux/native/pauseengine/pauseengine.c line 68:
> 
>> 66:         fclose(pidfile);
>> 67: 
>> 68:         printf(PAUSEENGINE "pausing the process, restore in another process to unpause it\n");
> 
> I would rather see all these logging messages going into `stderr`.

Warp prints its "Checkpoint successful" message to stout IIRC, then this should.go there too since it is essentially the same thing. We can make it disable-able via `-XX:CRaCEngineOptions=args=-quiet` for example.

-------------

PR Review Comment: https://git.openjdk.org/crac/pull/239#discussion_r2177144915