Improve type (de)serialization instability debugging

Improve type (de)serialization instability debugging

When debugging an issue uncovered by performing self comparison (abidw
--abidiff <binary>) I realized that I needed a stronger verification
of canonical types changing between type serialization and type
de-serialization.  Namely, when a type T with canonical type C is
serialized, its de-serialized type should still have the same
canonical type C.  Otherwise, it means some "type instability" took
place during serialization and de-serialization.

This patch implements that verification and also cleans up things
that came across while working on adding this debugging check.

	* include/abg-fwd.h (is_non_canonicalized_type): Declare new
	function.
	* src/abg-ir-priv.h: Include abg-corpus.h
	(environment::priv::pointer_type_id_map_): Fix comment.
	(environment::priv::check_canonical_type_from_abixml_during_self_comp):
	Define new member function.
	* src/abg-ir.cc (unmark_types_as_being_compared): Factorize this
	from ...
	(return_comparison_result): ... here.  Also, add a parameter to
	control whether this function should perform the "canonical type
	propagation optimization" or not.  By default the optimization is
	performed.  This can be changed for debugging purposes later.
	(type_base::get_canonical_type_for): Re-organise the self
	comparison debugging process to invoke the new function
	environment::priv::check_canonical_type_from_abixml_during_self_comp
	each time a canonical type is computed, in addition to doing the
	previous verification that was done when no canonical type was
	found.  Emit better error messages.
	(is_non_canonicalized_type): Rename the static function
	is_allowed_non_canonicalized_type into this and make it
	non-static.
	(hash_as_canonical_type_or_constant): Adjust.
	* src/abg-reader.cc (maybe_map_type_with_type_id): Define new
	static function.
	(read_context::maybe_check_abixml_canonical_type_stability):
	Ignore types that were not canonicalized.
	(read_corpus_from_input): Set the origin of the corpus early
	enough so that it's available to the canonicalizer even for types
	being canonicalized early.
	(MAYBE_MAP_TYPE_WITH_TYPE_ID): Factorize this macro out of ...
	(build_type): ... this.  That macro is defined only when debugging
	self comparison.
	(build_array_type_def): Map the read subrange type with its
	type-id.
	(handle_{type_decl, qualified_type, pointer_type_def,
	reference_type_def, function_type, array_type_def,enum_type_decl,
	typedef_decl, class_decl, union_decl}): Map the read type with its
	type-id.
	(load_canonical_type_ids): Ignore non-canonicalized types that
	which ids were saved in the type-id file.
	* src/abg-writer.cc (write_type_record): Factorize from ...
	(write_canonical_type_ids): ... here.  Don't forget to write the
	type-ids of decl-only types.  This can be useful for eye
	inspection.
	* tools/abidw.cc (load_corpus_and_write_abixml): Wait until the
	end of the function before removing the type-id file.  This can be
	useful for eye inspection.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>