Bug 24787 - Filter out enum changes into compatible integer types

Bug 24787 - Filter out enum changes into compatible integer types

Libabigail's filtering engine fails to recognize an enum changing into
a compatible integer (or vice versa) as a harmless change.

This patch fixes that.

	* include/abg-comparison.h (peel_typedef_or_qualified_type_diff):
	Declare new function.
	(peel_pointer_or_qualified_type_diff): Rename
	peel_pointer_or_qualified_type into this.
	* include/abg-fwd.h (is_enum_type): Declare a new overload for
	type_or_decl_base*.
	* src/abg-comp-filter.cc (has_harmless_enum_to_int_change): Define
	new static function.
	* src/abg-comparison.cc (categorize_harmless_diff_node): Use the
	new has_harmless_enum_to_int_change here.
	(peel_pointer_or_qualified_type_diff): Renamed
	peel_pointer_or_qualified_type into this.
	(is_diff_of_basic_type): Adjust.
	(peel_typedef_or_qualified_type_diff): Define new function.
	* test-diff-filter/PR24787-lib{one, two}.so: New test input
	binaries.
	* test-diff-filter/PR24787-{one, two}.c: Source files of the test
	input binaries above.
	* test-diff-filter/PR24787-report-0.txt: Test output reference.
	* tests/data/Makefile.am: Add the new testing material to source
	distribution.
	* tests/test-diff-filter.cc (in_out_specs): Add the new test to
	the test harness.

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