In shell: || false and && true are no-ops. So your little trick can be written:

clean::
        # Make sure we strip out non-DFSG demo files from the orig.tar.gz
        [ ! -f demo/qr-library.rb -a ! -f demo/qr-language.rb ]
        [ $$(md5sum images/bluesmoke.jpg | cut -f 1 -d ' ') == 0586eca5af7523ab871609eceb44724a ]
        [ $$(md5sum images/chunkybacon.jpg | cut -f 1 -d ' ') == a000b1917142ce332fd3474f0722cd6f ]
        [ $$(md5sum images/chunkybacon.png | cut -f 1 -d ' ') == 927feec1cbbf23c4d89a4a5ad88e6d0f ]