ref: 1e0f5fed0c530ac7dce561e2334ef3a0f7475507 dir: /builtins.arm64.s/
TEXT __builtin_ctz(SB),1,$0 RBITW R0, R0 CLZW R0, R0 RETURN TEXT __builtin_clz(SB),1,$0 CLZW R0, R0 RETURN TEXT __builtin_clzll(SB),1,$0 CLZ R0, R0 RETURN