Add sysSocket fallback (revert 7c1157f)

src/net/sock_windows.go

@@ -20,6 +20,20 @@ func maxListenerBacklog() int {
 func sysSocket(family, sotype, proto int) (syscall.Handle, error) {
 	s, err := wsaSocketFunc(int32(family), int32(sotype), int32(proto),
 		nil, 0, windows.WSA_FLAG_OVERLAPPED|windows.WSA_FLAG_NO_HANDLE_INHERIT)
+	if err == nil {
+		return s, nil
+	}
+	// WSA_FLAG_NO_HANDLE_INHERIT flag is not supported on some
+	// old versions of Windows, see
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/ms742212(v=vs.85).aspx
+	// for details. Just use syscall.Socket, if windows.WSASocket failed.
+	// See ../syscall/exec_unix.go for description of ForkLock.
+	syscall.ForkLock.RLock()
+	s, err = socketFunc(family, sotype, proto)
+	if err == nil {
+		syscall.CloseOnExec(s)
+	}
+	syscall.ForkLock.RUnlock()
 	if err != nil {
 		return syscall.InvalidHandle, os.NewSyscallError("socket", err)
 	}