ir: Tighten the test for anonymous data member

In is_anonymous_data_member(), we only test that the name of the data
member is empty; we forget to test that decl_base::get_is_anonymous()
is true.  This might make us wrongly think that a data member is
anonymous in cases like in the equals() function for var_decl, where
we temporarily set the name of the compared var_decl to "" before
invoking the decl_base::operator==.  We do this to perform the
comparison by not taking into account the name of the variable.

This hasn't yet happened on the binaries of the regression test suite,
but it's definitely wrong so I am fixing it here.

	* src/abg-ir.cc: (is_anonymous_data_member): Consider
	decl_base::get_is_anonymous as well.

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

src/abg-ir.cc

@@ -5474,6 +5474,7 @@ bool
 is_anonymous_data_member(const var_decl& d)
 {
   return (is_data_member(d)
+	  && d.get_is_anonymous()
 	  && d.get_name().empty()
 	  && is_class_or_union_type(d.get_type()));
 }