Add -mavx2 to TARGET=HASWELL builds
Add -mavx2 to TARGET=HASWELL builds

to leverage improvements from PR#1921
xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS