Fix bug in Makefile

Use original Makefile shows error when debugging:

```
gdb selected architecture aarch64 is not compatible with reported target architecture arm

```

Work for me now using this patch
```
diff Makefile.bak Makefile
142c142
<       @qemu-system-x86_64 -m 16M -boot a -fda Image -hda $(HDA_IMG) -s -S
---
>       @qemu-system-i386 -m 16M -boot a -fda Image -hda $(HDA_IMG) -s -S
```