Filter top cv qualifier changes on function parameter types

Filter top cv qualifier changes on function parameter types

When the type of a function parameter sees its top CV qualifier
change, that should never negatively affect ABI compliance.

So this patch filters out top cv qualifier changes on function
parameter types, by default.

	* include/abg-comparison.h (enum diff_category): Add a new
	FN_PARM_TYPE_TOP_CV_CHANGE_CATEGORY enumerator.  "Or" the
	enumerator to the EVERYTHING_CATEGORY enumerator.
	* src/abg-comp-filter.cc (has_fn_parm_type_cv_qual_change): Define
	new static function.
	(categorize_harmless_diff_node): Categorize changes to top cv
	qualifiers on function parameter types into the new
	FN_PARM_TYPE_TOP_CV_CHANGE_CATEGORY.
	* src/abg-comparison.cc (get_default_harmless_categories_bitmap):
	Add the new FN_PARM_TYPE_TOP_CV_CHANGE_CATEGORY category to the
	set of harmless categories.
	(operator<<(ostream&, diff_category)): Adjust to serialize
	the new FN_PARM_TYPE_TOP_CV_CHANGE_CATEGORY.
	* tests/data/test-diff-filter/libtest40-v0.so: New test input binary.
	* tests/data/test-diff-filter/libtest40-v1.so: Likewise.
	* tests/data/test-diff-filter/test40-report-0.txt: New test
	reference output.
	* tests/data/test-diff-filter/test40-v0.cc: Source code of the
	test binary above.
	* tests/data/test-diff-filter/test40-v1.cc: Likewise.
	* tests/data/Makefile.am: Add the new test material above to
	source distribution.
	* tests/test-diff-filter.cc (in_out_specs): Add new binaries to
	compare.
	* tests/data/test-diff-filter/test30-pr18904-rvalueref-report0.txt:
	Adjust.
	* tests/data/test-diff-filter/test30-pr18904-rvalueref-report1.txt:
	Likewise.
	* tests/data/test-diff-filter/test35-pr18754-no-added-syms-report-0.txt:
	Likewise.
	* tests/data/test-diff-filter/test35-pr18754-no-added-syms-report-1.txt:
	Likewise.

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