[Libguestfs] Libguestfs (1.22.6) driver/changes for mingw/win32

Hi, I attached the changes I made to a vanilla libguestfs-1.22.6 in order to make it work in mingw/win32. Added is also the patch required to make QEMU compatible (add a command to QMP that lists the supported devices (the regilat way you do it print it to stderr, which is difficult to redirect in win32)). This is done on behalf of Intel Corp. Thanks, Or (oberon in irc)