[clang] [llvm] [ARM] Add support for Windows SEH (PR #184953)

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kristibektashi wrote:

> @kristibektashi Thanks for the deep insights!
> 
> That said, my current use case is just kernel-mode SEH, so I guess non-Thumb is not really involved, similar to how C++ `try`/`catch` is not in scope for this PR.
> 
> I believe the reviewers, myself, and the agents behind me all agree that we should keep this PR as small as meaningfully possible.
> 
> Right now I am addressing the feedback - these are real problems, and I am trying to fix them as well as ensuring that the related tests pass.

I agree with you entirely, this should be a separate issue. With MSVC removing ARM32 support, right now said issue is more relevant than ever. However one issue at a time is the best call.

https://github.com/llvm/llvm-project/pull/184953