Use closesocket() for closing sockets under MSW

If accepting a socket connection failed, wxSocketImpl::Accept() used
close() to close the socket even under MSW, but it can be only used for
the file descriptors there and closesocket() must be used instead for
the sockets.

Add new (private) wxCloseSocket define and use it both here, to fix the
bug, and elsewhere to make the code more clear.

Closes #18407.

include/wx/unix/private/sockunix.h

@@ -23,6 +23,8 @@
 
 #include "wx/private/fdiomanager.h"
 
+#define wxCloseSocket close
+
 class wxSocketImplUnix : public wxSocketImpl,
                          public wxFDIOHandler
 {
@@ -64,7 +66,7 @@ private:
     {
         DisableEvents();
 
-        close(m_fd);
+        wxCloseSocket(m_fd);
     }
 
     virtual void UnblockAndRegisterWithEventLoop() wxOVERRIDE