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

[Connor Sughrue via llvm-commits]

cpsughrue wrote:

> 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.

Still trying to figure out the root cause but the jist of the issue is that the below code does not fail
```
  llvm::handleAllErrors(std::move(Err), [&](const llvm::StringError &SE) {
    ASSERT_EQ(0,1);
  });
```
The raw_socket_stream FILE_DESCRIPTOR_CLOSED test should fail but wrapping a gtest macro in llvm::handleAllErrors seems to "silence" it.



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