Implement proper type conversion in native compiler

Implement proper type conversion in native compiler

* src/comp.c (enum cast_kind_of_type): Remove.
(comp_t): Add cast_ptr_to_int, cast_int_to_ptr, remove
cast_type_sizes, cast_type_kind, cast_type_names, cast_union_fields,
cast_union_field_biggest_type.
(emit_coerce): Remove check for type size.
(struct cast_type): Remove bytes_size.
(define_type_punning): New function.
(define_cast_from_to): Implement proper type conversion.
(define_cast_functions): Adjust.  (bug#50230)