[Crashlytics] Mach IPC identity protected address backwards compatibility

[themiswang]

Follow up for #15612
Since MacOS 10.5 and 11 does not have identity protected behavior option, we need to fall back to default behavior for backward compatibility.

#15393

#no-changelog

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[themiswang]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds backward compatibility for Mach exception handling on older macOS versions by falling back to EXCEPTION_DEFAULT behavior. The changes are well-structured, using a union to handle different message formats and a behavior field to control the logic.

I've identified a critical bug where the code for finding the crashed thread (FIRCLSCrashedThreadLookup) incorrectly handles the new EXCEPTION_DEFAULT case, which could lead to a crash. I've also suggested refactoring to reduce code duplication and removing some leftover development comments. Please address the critical issue before merging.

[themiswang]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly adds backward compatibility for older macOS versions by falling back to EXCEPTION_DEFAULT behavior for the Mach exception handler. The use of a union for different message formats and propagating the behavior flag is well done. However, I've identified a critical bug in FIRCLSCrashedThreadLookup where it fails to handle the EXCEPTION_DEFAULT case, which would prevent crash reporting on older macOS versions. I've provided a detailed explanation and a fix for this issue. Additionally, I've included a minor suggestion to improve logging for better debugging.

[themiswang]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly implements backward compatibility for Mach exception handling on older macOS versions by introducing a fallback to EXCEPTION_DEFAULT behavior. The use of a union to manage different message structures is appropriate. The code is generally well-structured, but I've pointed out a minor opportunity for code deduplication to improve maintainability, along with a small style fix.