Avoid generating vshiftn for newer llvms
Avoid generating vshiftn for newer llvms


Former-commit-id: d10caf33718234507972e6b4cba8e1bb0ba3fffa
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide