Turn while loop into do-while, we know it will be executed at least once.
Turn while loop into do-while, we know it will be executed at least once.

[r28147]

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