Bug 24139 - Support suppressing some enumerator changes

Bug 24139 - Support suppressing some enumerator changes

This patch teaches the suppression specification subsystem how to
ignore changes of some enumerators in particular.

The patch adds a new property to the [suppress_type] section which is:

    changed_enumerators = enumerator1, enumerator2, etc

This property is taken into accound iff the current suppress_type does
have the 'type_kind = enum' property.

Changes to enum types that match the new 'changed_enumerators'
property are suppressed.

	* doc/manuals/libabigail-concepts.rst: Document the new
	'changed_enumerators' property.
	* include/abg-suppression.h
	(type_suppression::{g, s}et_changed_enumerator_names): Declare two
	new member functions.
	* src/abg-suppression-priv.h
	(type_suppression::priv::changed_enumerator_names_): Add a new
	data member.
	* src/abg-suppression.cc
	(type_suppression::{g,s}et_changed_enumerator_names): Define two
	new member functions.
	(type_suppression::suppresses_diff): Support evaluating the new
	'changed_enumerators = <vector of changed enumerators>'.
	(read_type_suppression): Read the new list
	property'changed_enumerators" and store it into the
	type_suppression using the new
	type_suppression::set_changed_enumerator_names ().
	* tests/data/test-diff-suppr/libtest4{0,1}-enumerator-changes-v{0,1}.so:
	Add new test inpujts.
	* tests/data/test-diff-suppr/test4{0,1}-enumerator-changes-0.suppr:
	Add a new suppr spec for this new test.
	* tests/data/test-diff-suppr/test4{0,1}-enumerator-changes-report-0.txt:
	The default report.
	* tests/data/test-diff-suppr/test4{0,1}-enumerator-changes-v{0,1}.cc:
	Add Source code of libtest4{0,1}-enumerator-changes-v{0,1}.so.
	* tests/data/Makefile.am: Add the test files above to source
	distribution.
	* tests/test-diff-suppr.cc: Add the test input files above to the
	harness.

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