WakeFD.cxx: use two sockets instead of pipe on Win32

Pipes aren't really pollable on Windows.
GLib emulates polling on pipes using separate reader/writer threads.
This adds significant overhead and keeps a strong dependency on GLib.

socketpair() function is absent on Windows as well.
We implement it here in a loose way.

src/GlobalEvents.cxx

@@ -78,7 +78,7 @@ GlobalEvents::Initialize()
 #ifndef G_OS_WIN32
 	GIOChannel *channel = g_io_channel_unix_new(wake_fd.Get());
 #else
-	GIOChannel *channel = g_io_channel_win32_new_fd(wake_fd.Get());
+	GIOChannel *channel = g_io_channel_win32_new_socket(wake_fd.Get());
 #endif
 
 	source_id = g_io_add_watch(channel, G_IO_IN,