c++/reflection: fixes for comparing reflections [PR125208]

c++/reflection: fixes for comparing reflections [PR125208]

This fixes two bugs:

1) crash in cp_tree_equal when comparing reflections with binfos;
cp_tree_equal doesn't handle those.  We're coming from
lookup_template_class -> spec_hasher::equal -> comp_template_args
-> cp_tree_equal.  We should use compare_reflections in cp_tree_equal.

2) the fix for 1) revealed that compare_reflections is buggy when
comparing two aliases: we shouldn't fall back to same_type_p
because given

   using A = int;
   using B = int;

^^A != ^^B should hold.

	PR c++/125208

gcc/cp/ChangeLog:

	* reflect.cc (compare_reflections): Use == when comparing two
	aliases.
	* tree.cc (cp_tree_equal) <case REFLECT_EXPR>: Use
	compare_reflections.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/alias3.C: New test.
	* g++.dg/reflect/bases_of5.C: New test.

Reviewed-by: Patrick Palka <ppalka@redhat.com>