btf: refactor and simplify implementation

btf: refactor and simplify implementation

This patch heavily refactors btfout.cc to take advantage of the
structural changes in the prior commits.

Now that inter-type references are internally stored as simply pointers,
all the painful, brittle, confusing infrastructure that was used in the
process of converting CTF type IDs to BTF type IDs can be thrown out.
This greatly simplifies the entire process of converting from CTF to
BTF, making the code cleaner, easier to read, and easier to maintain.

In addition, we no longer need to worry about destructive changes in
internal data structures used commonly by CTF and BTF, which allows
deleting several ancillary data structures previously used in btfout.cc.

This is nearly transparent, but a few improvements have also been made:

 1) BTF_KIND_FUNC records are now _always_ constructed at early_finish,
    allowing us to construct records even for functions which are later
    inlined by optimizations. DATASEC entries for functions are only
    constructed at late_finish, to avoid incorrectly generating entries
    for functions which get inlined.

 2) BTF_KIND_VAR records and DATASEC entries for them are now always
    constructed at (late) finish, which avoids cases where we could
    incorrectly create records for variables which were completely
    optimized away.  This fixes PR debug/113566 for non-LTO builds.
    In LTO builds, BTF must be emitted at early_finish, so some VAR
    records may be emitted for variables which are later optimized away.

 3) Some additional assembler comments have been added with more
    information for debugging.

gcc/
	* btfout.cc (struct btf_datasec_entry): New.
	(struct btf_datasec): Add `id' member.  Change `entries' to use
	new struct btf_datasec_entry.
	(func_map): New hash_map.
	(max_translated_id): New.
	(btf_var_ids, btf_id_map, holes, voids, num_vars_added)
	(num_types_added, num_types_created): Delete.
	(btf_absolute_var_id, btf_relative_var_id, btf_absolute_func_id)
	(btf_relative_func_id, btf_absolute_datasec_id, init_btf_id_map)
	(get_btf_id, set_btf_id, btf_emit_id_p): Delete.
	(btf_removed_type_p): Delete.
	(btf_dtd_kind, btf_emit_type_p): New helpers.
	(btf_fwd_to_enum_p, btf_calc_num_vbytes): Use them.
	(btf_collect_datasec): Delete.
	(btf_dtd_postprocess_cb, btf_dvd_emit_preprocess_cb)
	(btf_dtd_emit_preprocess_cb, btf_emit_preprocess): Delete.
	(btf_dmd_representable_bitfield_p): Adapt to type reference changes
	and delete now-unused ctfc argument.
	(btf_asm_datasec_type_ref): Delete.
	(btf_asm_type_ref): Adapt to type reference changes, simplify.
	(btf_asm_type): Likewise. Mark struct/union types with bitfield
	members.
	(btf_asm_array): Adapt to data structure changes.
	(btf_asm_varent): Likewise.
	(btf_asm_sou_member): Likewise. Ensure non-bitfield members are
	correctly re-encoded if struct or union contains any bitfield.
	(btf_asm_func_arg, btf_asm_func_type, btf_asm_datasec_entry)
	(btf_asm_datasec_type): Adapt to data structure changes.
	(output_btf_header): Adapt to other changes, simplify type
	length calculation, add info to assembler comments.
	(output_btf_vars): Adapt to other changes.
	(output_btf_strs): Fix overlong lines.
	(output_asm_btf_sou_fields, output_asm_btf_enum_list)
	(output_asm_btf_func_args_list, output_asm_btf_vlen_bytes)
	(output_asm_btf_type, output_btf_types, output_btf_func_types)
	(output_btf_datasec_types): Adapt to other changes.
	(btf_init_postprocess): Delete.
	(btf_output): Change to only perform output.
	(btf_add_const_void, btf_add_func_records): New.
	(btf_early_finish): Use them here. New.
	(btf_datasec_push_entry): Adapt to data structure changes.
	(btf_datasec_add_func, btf_datasec_add_var): New.
	(btf_add_func_datasec_entries): New.
	(btf_emit_variable_p): New helper.
	(btf_add_vars): Use it here. New.
	(btf_type_list_cb, btf_collect_translated_types): New.
	(btf_assign_func_ids, btf_late_assign_var_ids)
	(btf_assign_datasec_ids): New.
	(btf_finish): Remove unused argument. Call new btf_late*
	functions and btf_output.
	(btf_finalize): Adapt to data structure changes.
	* ctfc.h (struct ctf_dtdef): Convert existing boolean flags to
	BOOL_BITFIELD and reorder.
	(struct ctf_dvdef): Add dvd_id member.
	(btf_finish): Remove argument from prototype.
	(get_btf_id): Delete prototype.
	(funcs_traverse_callback, traverse_btf_func_types): Add an
	explanatory comment.
	* dwarf2ctf.cc (ctf_debug_finish): Remove unused argument.
	* dwarf2ctf.h: Analogous change.
	* dwarf2out.cc: Likewise.