stdc_trailing_zeros_uc
return (stdc_trailing_zeros_uc(~uc));
return (stdc_trailing_zeros_uc(uc) + 1);
.so_uc = stdc_trailing_zeros_uc,
char(*)[1]: stdc_trailing_zeros_uc(val), \
extern unsigned int stdc_trailing_zeros_uc(unsigned char) _C23_UNSEQ_ATTR;