Better support for enum diffs

Better support for enum diffs

	* include/abg-comparison.h (changed_enumerator_type): New typedef.
	(diff_category::{HARMLESS_ENUM_CHANGE_CATEGORY}): New enumerator.
	* src/abg-comp-filter.cc (has_type_size_change)
	(has_enumerator_insertion, has_enumerator_removal_or_change)
	(has_harmful_enum_change): New functions.
	(harmless_filter::visit): Categorize enumerator insertions that
	don't change the size of the type into HARMLESS_ENUM_CHANGE_CATEGORY.
	(harmful_filter::visit): Categorize enumerator removal or any enum
	change that changes the size of the type into
	SIZE_OR_OFFSET_CHANGE_CATEGORY.
	* src/abg-comparison.cc (enumerator_value_comp)
	(changed_enumerator_comp): New types.
	(sort_enumerators, sort_changed_enumerators): New static
	functions.
	(enum_diff::report): Sort enum related reports by the value of the
	enumerators.
	* src/abg-dwarf-reader.cc (build_enum_type): Name anonymous enums
	as __anonymous_enum__.
 	* tools/bidiff.cc (set_diff_context_from_opts): Add
	abigail::comparison::HARMLESS_ENUM_CHANGE_CATEGORY into the harmless
	stuff camp.
	* tests/data/test-diff-dwarf/test15-enum-report.txt: New test
	input.
	* tests/data/test-diff-dwarf/test15-enum-v1.o: Likewise.
	* tests/data/test-diff-dwarf/test15-enum-v0.o: Likewise.
	* tests/data/test-diff-dwarf/test15-enum-v0.cc: Source code for
	test input.
	* tests/data/test-diff-dwarf/test15-enum-v1.cc: Likewise.

	* tests/data/test-diff-filter/test19-enum-report-0.txt: New test input.
	* tests/data/test-diff-filter/test19-enum-report-1.txt: Likewise.
	* tests/data/test-diff-filter/test19-enum-v0.o: Likewise.
	* tests/data/test-diff-filter/test19-enum-v1.o: Likewise.
	* tests/data/test-diff-filter/test19-enum-v0.cc: Source code for
	test input.
	* tests/data/test-diff-filter/test19-enum-v1.cc: Likewise.
	* tests/test-diff-dwarf.cc: Run this test harness on the new test
	inputs above.
	* tests/test-diff-filter.cc: Likewise.
	* tests/Makefile.am: Add the new files above to the source distribution.

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