Added local optimization: Mux(a < 0, 0, 0xFFFFFFFF) => a >>s 31.
Added local optimization: Mux(a < 0, 0, 0xFFFFFFFF) => a >>s 31.

Also added Mux(a >= 0, 0, 0xFFFFFFFF) => ~a >>s 31.

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