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

[Trung Nguyen via cfe-commits]

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trungnt2910 wrote:

Yes, it seems like `clang` is already emitting the required unwinding metadata in the binaries, possibly for ABI compatibility with other tools like `libunwind` - it just does not know how to convert special IR instructions that handles `__try`/`__except`/`__finally` into native opcodes.

As for why it looks Thumb-specific, I believe it is because Windows NT on ARM is Thumb-only.

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