[llvm] [LLVM][Cygwin] add workaround for blocking connect/accept in AF_UNIX sockets (PR #140353)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo approved this pull request.

LGTM, but please add the reference links (from the later comment you posted) in the PR description so they'll end up in the commit message. After reading the commit itself I had questions about exactly that, which those links explained, so I think they're essential for later understanding of this commit.

https://github.com/llvm/llvm-project/pull/140353