[llvm] [llvm][Support] ListeningSocket::accept returns operation_canceled if FD is set to -1 (PR #89479)

[Michael Spencer via llvm-commits]

https://github.com/Bigcheese commented:

This looks correct with some minor comments, but it would be good to figure out why the existing shutdown test already returned `std::errc::operation_canceled`, but the module build daemon was seeing `std::errc::bad_file_descriptor` on shutdown.

https://github.com/llvm/llvm-project/pull/89479