Better detection of void* to something* change

Better detection of void* to something* change

Whenever a void* pointer changes to a T* pointer, we already consider
that change to be ABI-compatible.  The issue though is that we don't
detect the case of foo* changing into T* where foo is typedef void
foo.  This patch fixes that.

	* include/abg-ir.h (is_void_type): Add a new overload that takes
	type_base*.
	* src/abg-ir.cc (is_void_type): Define the new overload that takes
	type_base*.
	(is_void_pointer_type): Look through typedefs in
	the pointed-to type.

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