[libunwind] [libunwind][Haiku] Fix signal frame unwinding (PR #135367)

[Jérôme Duval via cfe-commits]

korli wrote:

> Yes, tested on `x86_64` and only `x86_64` (though support for other archs can be added by as easy as defining a few offsets and registers). Requires Haiku `hrev58811` to fully work with `tests/signal_unwind.pass.cpp`.
> 
> This is also the same implementation used in my debugger ports for Haiku.

Does it build on r1beta5?

https://github.com/llvm/llvm-project/pull/135367