[libunwind] libunwind: Implement the unw_strerror function for better nongnu libunwind compatibility (PR #160887)

[Gleb Popov via cfe-commits]

arrowd wrote:

> you could probably piggyback on bad_unwind_info.pass.cpp's second assert.

Turns out it isn't possible. `unw_step` returns a positive value in case of success or 0 if there is nowhere to step. The nongnu libunwind's manpage says that it also may return some error codes, but it is impossible for LLVM libunwind if I read the code correctly.

Would you like me to create a separate testcase or let's just skip it?

https://github.com/llvm/llvm-project/pull/160887