This patch changes the lowering for the following builtins to emit
calls to the new aarch64.sve.###.u intrinsics.
svabd_x svabd_n_x svadd_x svadd_n_x svasr_x svasr_n_x svdiv_x svdiv_n_x svdivr_x svdivr_n_x svlsl_x svlsl_n_x svlsr_x svlsr_n_x svmax_x svmax_n_x svmin_x svmin_n_x svmul_x svmul_n_x svmulh_x svmulh_n_x svsub_x svsub_n_x svsubr_x svsubr_n_x
Depends on D141938
nit is it worth adding a bit hasUndefVariant and doing !if (hasUndefVariant, intrinsic # "_u", intrinsic)?