ref: 065e6150c3b727a3dc15647609e6a4904c79ee18 dir: /builtins_plan9_amd64.s/
TEXT __builtin_clz(SB),1,$0 BYTE $0x0F; BYTE $0xBD; BYTE $0xC5 /* BSRL RARG, AX */ XORL $31, AX RET