Libunwind sandbox no longer needs to join sandboxee's userns.
This cleans up a lot of special handling for the libunwind sandbox.
PiperOrigin-RevId: 503140778
Change-Id: I020ea3adda05ae6ff74137b668a5fa7509c138f8
Follow-up changes might be required to fully fix up the contrib sandboxes.
PiperOrigin-RevId: 482475998
Change-Id: Iff631eb838a024b2f047a1be61bb27e35a8ff2f4
This change should make it less confusing where utility code comes from.
Having it in two places made sense when we were debating whether to publish
Sandbox2 separately, but not any longer.
Follow-up changes will move `sandbox2/util.h` and rename the remaining
`sandbox2/util` folder.
PiperOrigin-RevId: 351601640
Change-Id: I6256845261f610e590c25e2c59851cc51da2d778
Sending -1 as fd will fail and take forkserver down.
This should not happen normally so turned it into a check.
PiperOrigin-RevId: 285391908
Change-Id: Idbb05004c36cb0be57be1bd26df1c57cecfb0019