get_canonical_type_for: restore environment better

get_canonical_type_for: restore environment better

The method type_base::get_canonical_type_for contains some logic which
temporarily changes a couple of control flags in the type's
environment. It then restores these, but not consistently.

This patch ensures the flags are restored unconditionally.

	* src/abg-ir.cc (get_canonical_type_for): Ensure the
	do_on_the_fly_canonicalization and
	decl_only_class_equals_definition flags are restored
	unconditionally.

Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>