Windows 10 [received support](https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/) for AF_UNIX sockets in Insider Build 17063. This merge request adds basic support for AF_UNIX sockets to ws2_32 and wineserver.
Of particular note is the difficulty in handling `sun_path`. Most of the functions that allow for translating Windows paths to Unix paths are not accessible from ws2_32. I considered the following options: * Pass the Windows path to wineserver and do the conversion there. * This is, as far as I can tell, not possible without major rearchitecting. wineserver does not have functions to translate Windows paths to Unix paths, for obvious reasons. * Obtain the current working directory of the requesting process and temporarily change directories to there. * This only handles relative paths and fails for absolute paths, UNC paths, etc. * Conditionally change directories based on whether the path is relative or not. * This is error-prone and wineserver does not have the requisite functions to do this cleanly.
I ultimately decided to pass the translated Unix path to wineserver, which changes directories to `dirname(path)`. It then provides `bind` and `connect` with `basename(path)`. This is not threadsafe, but wineserver is not (currently) multithreaded.
Abstract sockets are supported by this patch.