Windows SEH unwind v3 support

[Andarwinux]

https://learn.microsoft.com/en-us/cpp/build/x64-unwind-information-v3?view=msvc-180

llvm/llvm-project#202809

APX on Windows/COFF require unwind v3 support.

[hpax]

This would be really, really great to get help with. I am not a Windows expert at all, and so it is very difficult for me to make sure to do this correctly.

This is up there with getting CFI support for (especially) DWARF generation done...

[SEt-t]

@hpax I have a near complete macro implementation of Unwind v1 and can create a PR if you want to start from that. It's quite scary but does work (and better than YASM support which has some errors in corner cases).

Though I'm not sure if such support should be done in macros or in base language. Main drawbacks of macro implementation are awful error messages in case something went wrong and requirement of several internal macros hanging there to keep necessary info.