mark labelled blocks as non-empty, preventing them to be removed
mark labelled blocks as non-empty, preventing them to be removed

[r15324]

MatzeB/libfirm,MatzeB/libfirm,8l/libfirm,MatzeB/libfirm,8l/libfirm,libfirm/libfirm,jonashaag/libfirm,MatzeB/libfirm,jonashaag/libfirm,davidgiven/libfirm,killbug2004/libfirm,killbug2004/libfirm,davidgiven/libfirm,davidgiven/libfirm,libfirm/libfirm,jonashaag/libfirm,davidgiven/libfirm,jonashaag/libfirm,8l/libfirm,killbug2004/libfirm,killbug2004/libfirm,libfirm/libfirm,davidgiven/libfirm,libfirm/libfirm,killbug2004/libfirm,8l/libfirm,davidgiven/libfirm,8l/libfirm,jonashaag/libfirm,killbug2004/libfirm,8l/libfirm,MatzeB/libfirm,MatzeB/libfirm,killbug2004/libfirm,8l/libfirm,MatzeB/libfirm,davidgiven/libfirm,libfirm/libfirm,jonashaag/libfirm,jonashaag/libfirm