Adding proper exiting and cleanup logic for singlefile createdump

[rcj1]

Closes dotnet/diagnostics#5245

This PR adds the proper exiting and cleanup logic for singlefile createdump. The exit() in the createdump child process ensures that the proper error messages are visible on the console and that said child processes do not accumulate in the system. This also necessitates a way to determine whether we are in the child process, before running destructors that unlink the diagnostics server socket (inherited from the parent and still needed by the parent). The code that would have ultimately been called on exit() is available here:

runtime/src/native/eventpipe/ds-ipc.c

Line 619 in 919597a

ds_ipc_close (port->ipc, is_shutdown, callback);

This logic is handled by g_ContinueCleanup which is set to true by default and set to false if we are in the child.

[Copilot]

Pull Request Overview

This PR ensures that the singlefile createdump child process exits cleanly without disturbing the parent’s diagnostic server socket.

• Introduces g_ContinueCleanup to skip cleanup in the forked child
• Guards PROCNotifyProcessShutdown with the new flag
• In the child branch of PROCCreateCrashDump, captures the callback’s return value, disables cleanup, and calls exit(...)

Comments suppressed due to low confidence (2)

src/coreclr/pal/src/thread/process.cpp:2266

• The new child‐process exit and cleanup gating behavior aren’t covered by existing tests. It would be valuable to add or update tests that fork and verify the child exits and the parent cleanup still runs.

            exit(callbackResult);

src/coreclr/pal/src/thread/process.cpp:218

• The global flag g_ContinueCleanup is accessed in both the normal and signal‐shutdown paths; consider making it volatile or using an atomic type to ensure thread‐safe reads and writes.

bool g_ContinueCleanup = true;