ref: a3856f049d188b971c0956b1b5cef350212f03a3 dir: /src/plan9_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