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

[Gleb Popov via cfe-commits]

arrowd wrote:

I just remembered that these strings are already present in the LLVM codebase: https://github.com/llvm/llvm-project/blob/a4015d98d2ad3faba12d8c1a82942330852b9efd/libunwind/include/libunwind.h#L54-L67

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