set_bit_field_width
$$ = set_bit_field_width($1, to_int_constant($3, true));
$$ = set_bit_field_width(NULL, to_int_constant($3, true));
$$ = set_bit_field_width($1, to_int_constant($3, true));
$$ = set_bit_field_width(NULL, to_int_constant($3, true));
sym_t *set_bit_field_width(sym_t *, int);