[llvm] [LLVM][Cygwin] Fix Signals compatibility with Cygwin API (PR #138117)

[via llvm-commits]

jeremyd2019 wrote:

Unrelated to this PR, but they really should be checking the return value of dladdr a few lines above and not trying to use the DL_info struct in case of error.  In Cygwin at least, it likely won't have written to dli_fname in that case.  I'm not firm enough in the specs involved in this case: In C I'd think you'd need to set the struct `= {0}` to make sure it's zeroed, but in C++ perhaps it and its members are default constructed and so zero rather than uninitialized?

https://github.com/llvm/llvm-project/pull/138117