Add qemu-override section

[pharra]

https://gitlab.com/qemu-project/qemu/-/issues/1015
nix demo

qemu-override = {
                device = {
                  alias = "hostdev0";
                  frontend = {
                    property = {
                      name = "x-vga";
                      type = "bool";
                      value = "true";
                    };
                  };
                };
              };

result

  <qemu:override>
    <qemu:device alias='hostdev0'>
      <qemu:frontend>
        <qemu:property name='x-vga' type='bool' value='true'/>
      </qemu:frontend>
    </qemu:device>
  </qemu:override>

[AshleyYakeley]

Thanks

[DrymarchonShaun]

doesn't this require all the device types in <devices> to optionally take <alias name="*"/>?