Generalize DIE source concept in DWARF reader

Generalize DIE source concept in DWARF reader

There are many functions in the DWARF reader that need to know if a
DIE comes from the primary or alternate debug info file.  Today, this
is conveyed by a boolean parameter.

This patch generalizes this idea of "source of DIE" by introducing a
new enum type named die_source that says where the DIE comes from.
This is to help later enable the introduction of a new kind of DIE
source.

The patch also introduces a new member function named
read_context::get_die_source to determine the source of a DIE.  This
helps remove the need of a die_source parameter on functions that
already take a DIE.  So this patch conceptually removes the die_source
parameter from many functions.

	* src/abg-dwarf-reader.cc (enum die_source): Define new enum.
	(operator++): Define new prefix increment operator for the
	die_source enum.
	(imported_unit_point::imported_unit_from_alt_di): Remove this
	data member.
	(imported_unit_point::imported_unit_die_source):
	New data member of type die_source.
	(read_context::primary_die_parent_map_): Renamed
	die_parent_map_ data member into this.
	(read_context::clear_per_corpus_data): Use the new
	clear_die_type_maps function, not die_type_map.  Also use the
	new clear_types_to_canonicalize overload that takes no
	parameter.
	(read_context::{get_die_source, clear_die_type_maps,
	clear_types_to_canonicalize}): New member functions.
	(build_ir_node_from_die, die_die_attribute, get_parent_die)
	(get_scope_for_die, build_namespace_decl_and_add_to_ir)
	(build_type_decl, build_enum_type)
	(build_class_type_and_add_to_ir, build_qualified_type)
	(build_pointer_type_def, build_reference_type)
	(build_function_type, build_array_type, build_typedef_type)
	(build_var_decl, build_function_decl): Remove the boolean
	parameter that was designating the source of the DIE.  If
	necessary, get the source of the DIE from inside the function
	using the new read_context::get_die_source.
	(read_debug_info_into_corpus): Adjust.
	(maybe_canonicalize_type, find_import_unit_point_between_dies)
	(maybe_canonicalize_type, read_context::{associate_die_to_decl,
	lookup_decl_from_die_offset, die_type_map, associate_die_to_type,
	lookup_type_from_die_offset, die_wip_classes_map,
	die_wip_function_types_map, is_wip_class_die_offset,
	is_wip_function_type_die_offset, types_to_canonicalize,
	schedule_type_for_late_canonicalization,
	canonicalize_types_scheduled, add_late_canonicalized_types_stats,
	perform_late_type_canonicalizing}): Take a die_source as the
	source of the DIE, not a boolean.  Adjust the code of the function
	accordingly.
	(read_context::{tu_die_imported_unit_points_map}): Modified
	this to make it take a die_source and return the appropriate
	map depending on the source.
	(read_context::build_die_parent_relations_under): Turn the
	non-member static function build_die_parent_relations_under
	into a member function.
	(read_context::build_die_parent_maps): Turn the non-member
	static function build_die_parent_maps into a member function.
	Make this function build a DIE -> parent map also for type
	DIEs that are in the .type_units section.

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