Bug 29977 - dwarf-reader: Fix canonical DIE propagation canceling

Bug 29977 - dwarf-reader: Fix canonical DIE propagation canceling

When canceling canonical DIE propagation, we wrongly assume that the
pair of DIEs being compared yield a COMPARE_RESULT_UNKNOWN result.
The reality is that it can also yield a COMPARE_RESULT_DIFFERENT
result, especially when we are looking at the first sub-type that
compares different and that triggered the canonical DIE propagation
canceling to begin with.

This can be reproduced by the command:

$ fedabipkgdiff --self-compare -a --from fc37 xorg-x11-server-Xvfb

Fixed thus.

	* src/abg-dwarf-reader.cc
	(offset_pairs_stack_type::cancel_canonical_propagated_type): The
	result of comparing the canonical-propagated types being canceled
	is either COMPARISON_RESULT_UNKNOWN or
	COMPARISON_RESULT_DIFFERENT.  Also, do not forget to update the
	cached value for the comparison of the depend types too.

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