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.
