[crac] RFR: 8361090: [CRaC] Make dev engines less confusing [v2]

[Timofei Pushkin]

> - 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

Timofei Pushkin has updated the pull request incrementally with one additional commit since the last revision:

  Log to stderr

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Changes:
  - all: https://git.openjdk.org/crac/pull/239/files
  - new: https://git.openjdk.org/crac/pull/239/files/e4d6832c..e87556e4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=239&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=239&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/crac/pull/239.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/239/head:pull/239

PR: https://git.openjdk.org/crac/pull/239