ldstopt: Use exchange() instead of set_irn_in() when a Sync has only a single operand left.
ldstopt: Use exchange() instead of set_irn_in() when a Sync has only a single operand left.

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