Make abidiff --harmless show harmless changes in unions

Make abidiff --harmless show harmless changes in unions

Since the previous commit filters out harmless changes inside unions,
this one allows those changes to be reported whenever the user runs
abidiff with the --harmless option.

The patch just displays the "before" and "after" of the union because
some of the harmless changes are not tracked anymore.

Because we want to display the before and after of the union we use
the function get_class_or_union_flat_representation.  The patch adds a
"qualified_name" boolean parameter to that function so that we can
choose to display union members names in a non-qualified fashion,
which is the natural way of displaying those names in the context of a
union (or class) representation.  Because
get_class_or_union_flat_representation uses
type_or_decl_base::get_pretty_representation, the patch has also added a
"qualified_name" boolean parameter to that function so that we can
choose to display names in a non-qualified manner.

	* include/abg-fwd.h (get_class_or_union_flat_representation): Add
	a "qualified_name" boolean parameter.
	* include/abg-ir.h ({type_or_decl_base, decl_base, type_decl,
	namespace_decl, array_type_def::subrange_type, array_type_def,
	enum_type_decl, typedef_decl, var_decl, function_decl,
	function_decl::parameter, function_type, method_type, class_decl,
	union_decl}::get_pretty_representation): Likewise.
	* src/abg-ir.cc ({type_or_decl_base, decl_base, type_decl,
	namespace_decl, array_type_def::subrange_type, array_type_def, enum_type_decl,
	typedef_decl, var_decl, function_decl, function_decl::parameter,
	function_type, method_type, class_decl, union_decl,
	}::get_pretty_representation): Adjust the code to emit qualified
	or non-qualified names depending on the new "qualified_name"
	boolean parameter.
	(get_class_or_union_flat_representation): Likewise.
	* src/abg-default-reporter.cc (default_reporter::report): Use
	get_class_or_union_flat_representation with the new
	"qualified_name" boolean set to false.
	* tests/data/test-diff-dwarf/test38-union-report-0.txt: Adjust.
	* tests/test-diff-filter.cc (in_out_specs): Run the test harness
	on test-PR24731-v{0,1}.o make abidiff use the --harmless option.

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