This PR implements `raw_socket_stream::read`, which overloads the base
class `raw_fd_stream::read`. `raw_socket_stream::read` provides a way to
timeout the underlying `::read`. The timeout functionality was not added
to `raw_fd_stream::read` to avoid needlessly increasing compile times
and allow for convenient code reuse with `raw_socket_stream::accept`,
which also requires timeout functionality. This PR supports the module
build daemon and will help guarantee it never becomes a zombie process.
If `::poll` returns and `FD` equals -1, then `ListeningSocket::shutdown`
has been called. So, regardless of any other information that could be
gleaned from `FDs.revents` or `PollStatus`, it is appropriate to return
`std::errc::operation_canceled`. `ListeningSocket::shutdown` copies
`FD`'s value to `ObservedFD` then sets `FD` to -1 before canceling
`::poll` by calling `::close(ObservedFD)` and writing to the pipe.
Improvements include
* Enable `ListeningSocket::accept` to timeout after a specified amount
of time or block indefinitely
* Enable `ListeningSocket::createUnix` to handle instances where the
target socket address already exists and differentiate between
situations where the existing file does and does not already have a
bound socket
* Doxygen comments
Functionality added for the module build daemon
---------
Co-authored-by: Michael Spencer <bigcheesegs@gmail.com>
AF_UNIX sockets were added to Windows 10 build 17063 in 2017, older
versions of Windows will fail this test.
Also add a lit config so lit tests using sockets can do:
// REQUIRES: unix-sockets
(It would be cool if unit tests could use lit available_features)
Also fix llvm-config test that didn't fail when new libs are added.
