ir: Avoid cancelling a "confirmed" propagated canonical type

ir: Avoid cancelling a "confirmed" propagated canonical type

When canonicalizing a type T at the IR level, the canonical type of T
(aka C(T)) can be deduced in two ways:

1/ Either T structurally (aka member-wise) compares equal to another
   T' which has a canonical type C(T').  In that case we deduce that
   C(T) equals C(T').

2/ Or, during the canonicalization of another type Y of which T is a
   sub-type, the comparison engine comes to compare T against a type
   T' that is already canonicalized and finds that T structurally
   compares equal to T'.  In that case we deduce that C(T) equals
   C(T'), even though we were canonicalizing Y in the first place.

In 2/ we C(T) is stored and so when comes the time to canonicalize T,
we already know C(T).

What happens in 2/ is called "canonical type propagation". Because the
canonical type of T' is propagated to T while canonicalizing Y.

There can be cases however where the propagated canonical type has to
be "cancelled".  This is described in the source code in abg-ir.cc in
the "@ref OnTheFlyCanonicalization" chapter of the doxygen
documentation.

There are also cases where the propagated canonical type has been
"confirmed", meaning, it cannot be cancelled anymore.

Unfortunately, there seems to be (wrong) cases where confirmed
propagated canonical types are being cancelled.  Oops.  That leads to
having types that are missing canonical types down the road.

This is exhibited by the self-comparison check of the
avr-binutils-2.39-1.fc36.armv7hl.rpm package (more precisely when
analyzing the 'objdump' binary from that package).  This was triggered
by the command:

$ fedabipkgdiff  --self-compare --from fc36 avr-binutils

This patch improves the book keeping around IR canonical type
propagation to avoid cancelling confirmed propagated canonical types.

It introduces a flag to the type_base::priv sub-object to track the
confirmation status of propagated canonical types.  It then updates
the book-keeping routines to make them avoid cancelling confirmed
propagated canonical types.

	* src/abg-ir-priv.h
	(type_base::priv::propagated_canonical_type_confirmed_): Define
	new data member.
	(type_base::priv::priv): Initialize it.
	(type_base::priv::{propagated_canonical_type_confirmed,
	set_propagated_canonical_type_confirmed}): Define new member
	functions.
	(type_base::priv::clear_propagated_canonical_type): Do not clear
	the propagated canonical type if it has been confirmed already.
	(type_base::priv::confirm_ct_propagation_for_types_dependant_on): Rename
	type_base::confirm_ct into this.  Mark the confirmed propagated
	types as being confirmed.
	(type_base::priv::confirm_ct_propagation): This is now a new member
	function that calls
	type_base::confirm_ct_propagation_for_types_dependant_on and that
	does the book-keeping that was being done in
	return_comparison_result.
	(type_base::priv::cancel_ct_propagation_for_types_dependant_on):
	Renamed type_base::priv::cancel_ct_propagation in this.
	(type_base::priv::cancel_ct_propagation): In this new one, call
	type_base::priv::cancel_ct_propagation_for_types_dependant_on. Perform here
	the book-keeping that was being done in return_comparison_result.
	Also, do not cancel a confirmed propagated canonical type.
	(type_base::priv::add_to_types_with_non_confirmed_propagated_ct):
	Define new member function.
	* src/abg-ir.cc (return_comparison_result): Consider only types
	with non-confirmed propagated canonical types for the
	non-confirmed type queue.  Also, only sub-types can be considered
	non-confirmed.  Split out some of the book-keeping into
	type_base::priv::{confirm_ct_propagation, cancel_ct_propagation}
	and call these instead.  Confirm the propagated canonical types of
	all types that remain after the comparison is fully done and is
	successful.
	(canonicalize): Assert the rule "The result of canonicalizing must
	always been a confirmed canonical type".

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