The current unwinding implementation on Haiku is messy and broken.
1. It searches weird paths for private headers, which is breaking builds
in consuming projects, such as dotnet/runtime.
2. It does not even work, due to relying on incorrect private offsets.
This commit strips all references to private headers and ports a working
signal frame implementation. It has been tested against
`tests/signal_unwind.pass.cpp` and can go pass the signal frame.
1d9ef8211f