Use size/alignment of class definition when requested on declaration

Use size/alignment of class definition when requested on declaration

Sometimes during hashing the "type sub-object" of a class can be
queried for its size or alignment.  In those case, if the class is a
declaration that happens to be accompanied with a definition, its the
size/alignment of the definition that we want, not the one of the
declaration, that is zero.  Otherwise, this can cause spurious hashing
changes between two class types that are otherwise equivalent modulo
the use of a class declaration.

This patch being part of a series that aims at fixing a number of type
hashing issues, the regression tests are adjusted at the end of the
series, not here.

	* include/abg-ir.h (type_base::{set_size_in_bits,
	set_alignment_in_bits}): Make these member functions virtual.
	(class_decl::{set_size_in_bits, get_size_in_bits,
	get_alignment_in_bits, set_alignment_in_bits}): Declare these
	virtual member functions.
	* src/abg-ir.cc (class_decl::{set_size_in_bits, get_size_in_bits,
	get_alignment_in_bits, set_alignment_in_bits}): Define these
	virtual functions.

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