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
- Use a `constexpr inline` string constant for the forkserver env var
- Add annotation for the comms channel mutex
PiperOrigin-RevId: 335395005
Change-Id: Ic058c19c3704f182aa7ed7b8e8964b2fc5082800