Update Simplify.cpp
Update Simplify.cpp

Don't normalize x >> 31 to x / (1 << 31). It overflows.

Fixes #975
jiawen/Halide,kgnk/Halide,dougkwan/Halide,adasworks/Halide,psuriana/Halide,adasworks/Halide,tdenniston/Halide,jiawen/Halide,ronen/Halide,kgnk/Halide,adasworks/Halide,dougkwan/Halide,tdenniston/Halide,jiawen/Halide,ronen/Halide,psuriana/Halide,ronen/Halide,psuriana/Halide,adasworks/Halide,ronen/Halide,tdenniston/Halide,dougkwan/Halide,tdenniston/Halide,jiawen/Halide,tdenniston/Halide,dougkwan/Halide,dougkwan/Halide,dougkwan/Halide,kgnk/Halide,ronen/Halide,kgnk/Halide,psuriana/Halide,adasworks/Halide,psuriana/Halide,tdenniston/Halide,ronen/Halide,kgnk/Halide,dougkwan/Halide,jiawen/Halide,kgnk/Halide,ronen/Halide,adasworks/Halide,tdenniston/Halide,adasworks/Halide,jiawen/Halide,ronen/Halide,tdenniston/Halide,adasworks/Halide,jiawen/Halide,dougkwan/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide