Clean the output of .bat files (#20913)

[aportale]

This prevents echoing out "set MYDIR=foo" and "goto FOUND_MYDIR" by prepending the lines with a "@".

[sbc100]

Sorry I didn't see this so I created a fix here: #20916

[sbc100]

One should not need to prefix commands inside the if/else branches with @ if the if itself is prefixed with @ (as in this case). While debugging this I confirmed that, for example, lines 33-37 don't need the @ prefix.

[aportale]

Thanks, your variant is the proper fix. And it works well, here:

:)

[sbc100]

Awesome!