[llvm] [llvm][Support] Add UNIX socket support (PR #73603)

[Shilei Tian via llvm-commits]

shiltian wrote:

Am I the only one getting the following error?
```
/home/ac.shilei.tian/Documents/vscode/llvm-project/llvm/lib/Support/raw_ostream.cpp: In static member function ‘static llvm::Expected<llvm::ListeningSocket> llvm::ListeningSocket::createUnix(llvm::StringRef, int)’:
/home/ac.shilei.tian/Documents/vscode/llvm-project/llvm/lib/Support/raw_ostream.cpp:1040:10: error: could not convert ‘ListenSocket’ from ‘llvm::ListeningSocket’ to ‘llvm::Expected<llvm::ListeningSocket>’
   return ListenSocket;
          ^~~~~~~~~~~~
```

https://github.com/llvm/llvm-project/pull/73603